chore: update Windows release notes for beta.18

windows/App.xaml

@@ -1,25 +1,30 @@
 <Application x:Class="ClaudeCheckerWindows.App"
              xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:po="http://schemas.microsoft.com/winfx/2006/xaml/presentation/options"
              ShutdownMode="OnExplicitShutdown">
     <Application.Resources>
-        <SolidColorBrush x:Key="BackgroundBrush"  Color="#F3F3F3"/>
+        <SolidColorBrush x:Key="BackgroundBrush"   Color="#F3F3F3" po:Freeze="False"/>
-        <SolidColorBrush x:Key="CardBrush"        Color="#FFFFFF"/>
+        <SolidColorBrush x:Key="CardBrush"         Color="#FFFFFF" po:Freeze="False"/>
-        <SolidColorBrush x:Key="AccentBrush"      Color="#F97316"/>
+        <SolidColorBrush x:Key="AccentBrush"       Color="#F97316" po:Freeze="False"/>
-        <SolidColorBrush x:Key="TextBrush"        Color="#1C1C1C"/>
+        <SolidColorBrush x:Key="TextBrush"         Color="#1C1C1C" po:Freeze="False"/>
-        <SolidColorBrush x:Key="SecondaryBrush"   Color="#6E6E6E"/>
+        <SolidColorBrush x:Key="SecondaryBrush"    Color="#6E6E6E" po:Freeze="False"/>
-        <SolidColorBrush x:Key="BorderBrush"      Color="#E0E0E0"/>
+        <SolidColorBrush x:Key="BorderBrush"       Color="#E0E0E0" po:Freeze="False"/>
-        <SolidColorBrush x:Key="BlueBrush"        Color="#0078D4"/>
+        <SolidColorBrush x:Key="BlueBrush"         Color="#0078D4" po:Freeze="False"/>
+        <SolidColorBrush x:Key="ButtonBrush"       Color="#FFFFFF" po:Freeze="False"/>
+        <SolidColorBrush x:Key="SurfaceBrush"      Color="#FAFAFA" po:Freeze="False"/>
+        <SolidColorBrush x:Key="BannerBgBrush"     Color="#E8F2FB" po:Freeze="False"/>
+        <SolidColorBrush x:Key="BannerBorderBrush" Color="#B3D6F5" po:Freeze="False"/>
 
         <Style x:Key="HeaderText" TargetType="TextBlock">
             <Setter Property="FontSize"   Value="10"/>
             <Setter Property="FontWeight" Value="SemiBold"/>
-            <Setter Property="Foreground" Value="{StaticResource SecondaryBrush}"/>
+            <Setter Property="Foreground" Value="{DynamicResource SecondaryBrush}"/>
             <Setter Property="FontFamily" Value="Segoe UI"/>
         </Style>
 
         <Style x:Key="PrimaryButton" TargetType="Button">
-            <Setter Property="Background"      Value="{StaticResource BlueBrush}"/>
+            <Setter Property="Background"      Value="{DynamicResource BlueBrush}"/>
             <Setter Property="Foreground"      Value="White"/>
             <Setter Property="BorderThickness" Value="0"/>
             <Setter Property="Padding"         Value="14,6"/>
@@ -48,10 +53,10 @@
         </Style>
 
         <Style x:Key="SmallButton" TargetType="Button">
-            <Setter Property="Background"      Value="#FFFFFF"/>
+            <Setter Property="Background"      Value="{DynamicResource ButtonBrush}"/>
-            <Setter Property="BorderBrush"     Value="{StaticResource BorderBrush}"/>
+            <Setter Property="BorderBrush"     Value="{DynamicResource BorderBrush}"/>
             <Setter Property="BorderThickness" Value="1"/>
-            <Setter Property="Foreground"      Value="{StaticResource TextBrush}"/>
+            <Setter Property="Foreground"      Value="{DynamicResource TextBrush}"/>
             <Setter Property="Padding"         Value="10,4"/>
             <Setter Property="FontSize"        Value="12"/>
             <Setter Property="FontFamily"      Value="Segoe UI"/>

windows/App.xaml.cs

@@ -17,7 +17,21 @@ public partial class App : Application
 
     protected override void OnStartup(StartupEventArgs e)
     {
+        var logPath = System.IO.Path.Combine(
+            Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
+            "ClaudeChecker", "startup_crash.txt");
+
+        AppDomain.CurrentDomain.UnhandledException += (_, ex) =>
+            System.IO.File.WriteAllText(logPath, ex.ExceptionObject?.ToString() ?? "unknown");
+
+        DispatcherUnhandledException += (_, ex) =>
+        {
+            System.IO.File.WriteAllText(logPath, ex.Exception?.ToString() ?? "unknown");
+            ex.Handled = false;
+        };
+
         base.OnStartup(e);
+        ThemeManager.Initialize();
         SetupTray();
         ScheduleTimer(ViewModel.RefreshInterval);
 

windows/Controls/GaugeControl.cs

@@ -21,6 +21,11 @@ public class GaugeControl : FrameworkElement
     public double Percent { get => (double)GetValue(PercentProperty); set => SetValue(PercentProperty, value); }
     public Brush  Accent  { get => (Brush)GetValue(AccentProperty);   set => SetValue(AccentProperty, value); }
 
+    public GaugeControl()
+    {
+        ThemeManager.ThemeChanged += InvalidateVisual;
+    }
+
     private const double StartAngleDeg = 135;
     private const double SweepDeg      = 270;
     private const double StrokeWidth   = 6;
@@ -31,8 +36,11 @@ public class GaugeControl : FrameworkElement
         var cy     = RenderSize.Height / 2;
         var radius = Math.Min(cx, cy) - StrokeWidth / 2 - 1;
 
+        var trackColor = ThemeManager.IsDark
+            ? Color.FromArgb(40, 255, 255, 255)
+            : Color.FromArgb(30, 0, 0, 0);
         DrawArc(dc, cx, cy, radius, StartAngleDeg, SweepDeg,
-            new Pen(new SolidColorBrush(Color.FromArgb(30, 0, 0, 0)), StrokeWidth));
+            new Pen(new SolidColorBrush(trackColor), StrokeWidth));
 
         if (Percent > 0)
             DrawArc(dc, cx, cy, radius, StartAngleDeg, SweepDeg * (Percent / 100.0),
@@ -40,18 +48,21 @@ public class GaugeControl : FrameworkElement
 
         var dpi = VisualTreeHelper.GetDpi(this).PixelsPerDip;
 
+        var textColor = ThemeManager.IsDark ? Color.FromRgb(0xF5, 0xF5, 0xF5) : Color.FromRgb(0x1C, 0x1C, 0x1C);
+        var subColor  = Color.FromRgb(0x9E, 0x9E, 0x9E);
+
         var pctText = new FormattedText(
             $"{(int)Math.Round(Percent)}%",
             CultureInfo.CurrentCulture, FlowDirection.LeftToRight,
             new Typeface(new FontFamily("Segoe UI"), FontStyles.Normal, FontWeights.Bold, FontStretches.Normal),
-            14, new SolidColorBrush(Color.FromRgb(0x1C, 0x1C, 0x1C)), dpi);
+            14, new SolidColorBrush(textColor), dpi);
         dc.DrawText(pctText, new Point(cx - pctText.Width / 2, cy - pctText.Height - 1));
 
         var sub = new FormattedText(
             "Updated\nnow",
             CultureInfo.CurrentCulture, FlowDirection.LeftToRight,
             new Typeface("Segoe UI"), 7,
-            new SolidColorBrush(Color.FromRgb(0x9E, 0x9E, 0x9E)), dpi)
+            new SolidColorBrush(subColor), dpi)
         {
             TextAlignment = TextAlignment.Center
         };

windows/PopupWindow.xaml

@@ -5,7 +5,7 @@
         Title="ClaudeChecker"
         Width="480" Height="660"
         WindowStartupLocation="CenterScreen"
-        Background="{StaticResource BackgroundBrush}"
+        Background="{DynamicResource BackgroundBrush}"
         FontFamily="Segoe UI"
         ShowInTaskbar="True"
         ResizeMode="NoResize">
@@ -16,7 +16,8 @@
 
             <!-- Update banner -->
             <Border x:Name="UpdateBanner" DockPanel.Dock="Top" Visibility="Collapsed"
-                    Background="#E8F2FB" BorderBrush="#B3D6F5" BorderThickness="0,0,0,1"
+                    Background="{DynamicResource BannerBgBrush}"
+                    BorderBrush="{DynamicResource BannerBorderBrush}" BorderThickness="0,0,0,1"
                     Cursor="Hand" MouseLeftButtonUp="UpdateBanner_Click">
                 <Grid Margin="16,10">
                     <Grid.ColumnDefinitions>
@@ -25,21 +26,21 @@
                         <ColumnDefinition Width="Auto"/>
                     </Grid.ColumnDefinitions>
                     <TextBlock Grid.Column="0" Text="⬇" FontSize="14"
-                               Foreground="{StaticResource BlueBrush}" VerticalAlignment="Center"/>
+                               Foreground="{DynamicResource BlueBrush}" VerticalAlignment="Center"/>
                     <StackPanel Grid.Column="1" Margin="10,0">
                         <TextBlock x:Name="UpdateBannerTitle" FontSize="12" FontWeight="SemiBold"
-                                   Foreground="{StaticResource TextBrush}"/>
+                                   Foreground="{DynamicResource TextBrush}"/>
                         <TextBlock Text="Click to view release notes and install."
-                                   FontSize="11" Foreground="{StaticResource SecondaryBrush}"/>
+                                   FontSize="11" Foreground="{DynamicResource SecondaryBrush}"/>
                     </StackPanel>
                     <Button Grid.Column="2" Content="Update" Style="{StaticResource SmallButton}"
-                            Foreground="{StaticResource BlueBrush}" Click="UpdateBanner_Click"/>
+                            Foreground="{DynamicResource BlueBrush}" Click="UpdateBanner_Click"/>
                 </Grid>
             </Border>
 
             <!-- Footer -->
-            <Border DockPanel.Dock="Bottom" BorderBrush="{StaticResource BorderBrush}"
+            <Border DockPanel.Dock="Bottom" BorderBrush="{DynamicResource BorderBrush}"
-                    BorderThickness="0,1,0,0" Background="#FAFAFA">
+                    BorderThickness="0,1,0,0" Background="{DynamicResource SurfaceBrush}">
                 <Grid Margin="12,8">
                     <Grid.ColumnDefinitions>
                         <ColumnDefinition Width="*"/>
@@ -54,7 +55,7 @@
                                      Width="12" Height="12" Visibility="Collapsed"
                                      Style="{x:Null}" Margin="0,0,6,0"/>
                         <TextBlock x:Name="LastUpdatedText" FontSize="11"
-                                   Foreground="{StaticResource SecondaryBrush}" VerticalAlignment="Center"/>
+                                   Foreground="{DynamicResource SecondaryBrush}" VerticalAlignment="Center"/>
                     </StackPanel>
                     <Button Grid.Column="1" Content="↻  Refresh"
                             Style="{StaticResource SmallButton}" Click="Refresh_Click"/>
@@ -71,17 +72,17 @@
 
         <!-- Settings panel -->
         <Border x:Name="SettingsPanel" Visibility="Collapsed"
-                Background="{StaticResource BackgroundBrush}">
+                Background="{DynamicResource BackgroundBrush}">
             <DockPanel>
-                <Border DockPanel.Dock="Top" BorderBrush="{StaticResource BorderBrush}"
+                <Border DockPanel.Dock="Top" BorderBrush="{DynamicResource BorderBrush}"
-                        BorderThickness="0,0,0,1" Background="#FAFAFA" Padding="12,10">
+                        BorderThickness="0,0,0,1" Background="{DynamicResource SurfaceBrush}" Padding="12,10">
                     <Grid>
                         <Button Content="← Back" HorizontalAlignment="Left"
                                 Style="{StaticResource SmallButton}" BorderThickness="0"
-                                Foreground="{StaticResource BlueBrush}" Background="Transparent"
+                                Foreground="{DynamicResource BlueBrush}" Background="Transparent"
                                 Click="BackFromSettings_Click"/>
                         <TextBlock Text="Settings" FontSize="14" FontWeight="SemiBold"
-                                   Foreground="{StaticResource TextBrush}"
+                                   Foreground="{DynamicResource TextBrush}"
                                    HorizontalAlignment="Center" VerticalAlignment="Center"/>
                     </Grid>
                 </Border>
@@ -90,13 +91,13 @@
                     <StackPanel Margin="20,16,20,20">
 
                         <TextBlock Text="AUTHENTICATION" Style="{StaticResource HeaderText}" Margin="0,0,0,8"/>
-                        <Border Background="{StaticResource CardBrush}" CornerRadius="6"
+                        <Border Background="{DynamicResource CardBrush}" CornerRadius="6"
-                                BorderBrush="{StaticResource BorderBrush}" BorderThickness="1"
+                                BorderBrush="{DynamicResource BorderBrush}" BorderThickness="1"
                                 Padding="14,12" Margin="0,0,0,16">
                             <StackPanel>
                                 <StackPanel x:Name="AuthPanel" Margin="0,0,0,10"/>
                                 <TextBlock Text="Your session is stored locally and persists across restarts."
-                                           FontSize="11" Foreground="{StaticResource SecondaryBrush}"
+                                           FontSize="11" Foreground="{DynamicResource SecondaryBrush}"
                                            TextWrapping="Wrap" Margin="0,0,0,10"/>
                                 <StackPanel Orientation="Horizontal">
                                     <Button x:Name="SignInButton" Content="Sign In"
@@ -111,8 +112,8 @@
                         </Border>
 
                         <TextBlock Text="UPDATE CHANNEL" Style="{StaticResource HeaderText}" Margin="0,0,0,8"/>
-                        <Border Background="{StaticResource CardBrush}" CornerRadius="6"
+                        <Border Background="{DynamicResource CardBrush}" CornerRadius="6"
-                                BorderBrush="{StaticResource BorderBrush}" BorderThickness="1"
+                                BorderBrush="{DynamicResource BorderBrush}" BorderThickness="1"
                                 Padding="14,12" Margin="0,0,0,16">
                             <Grid>
                                 <Grid.ColumnDefinitions>
@@ -121,9 +122,9 @@
                                 </Grid.ColumnDefinitions>
                                 <StackPanel>
                                     <TextBlock Text="Beta updates" FontSize="12" FontWeight="SemiBold"
-                                               Foreground="{StaticResource TextBrush}"/>
+                                               Foreground="{DynamicResource TextBrush}"/>
                                     <TextBlock Text="Receive early access builds — may be less stable"
-                                               FontSize="11" Foreground="{StaticResource SecondaryBrush}"/>
+                                               FontSize="11" Foreground="{DynamicResource SecondaryBrush}"/>
                                 </StackPanel>
                                 <CheckBox Grid.Column="1" x:Name="BetaToggle" VerticalAlignment="Center"
                                           Checked="BetaToggle_Changed" Unchecked="BetaToggle_Changed"/>
@@ -131,8 +132,8 @@
                         </Border>
 
                         <TextBlock Text="AUTO-REFRESH" Style="{StaticResource HeaderText}" Margin="0,0,0,8"/>
-                        <Border Background="{StaticResource CardBrush}" CornerRadius="6"
+                        <Border Background="{DynamicResource CardBrush}" CornerRadius="6"
-                                BorderBrush="{StaticResource BorderBrush}" BorderThickness="1"
+                                BorderBrush="{DynamicResource BorderBrush}" BorderThickness="1"
                                 Padding="14,12" Margin="0,0,0,16">
                             <Grid>
                                 <Grid.ColumnDefinitions>
@@ -140,15 +141,15 @@
                                     <ColumnDefinition Width="Auto"/>
                                 </Grid.ColumnDefinitions>
                                 <TextBlock Text="Refresh interval" FontSize="12" FontWeight="SemiBold"
-                                           Foreground="{StaticResource TextBrush}" VerticalAlignment="Center"/>
+                                           Foreground="{DynamicResource TextBrush}" VerticalAlignment="Center"/>
                                 <ComboBox Grid.Column="1" x:Name="RefreshPicker" Width="100"
                                           SelectionChanged="RefreshPicker_Changed"/>
                             </Grid>
                         </Border>
 
                         <TextBlock Text="ABOUT" Style="{StaticResource HeaderText}" Margin="0,0,0,8"/>
-                        <Border Background="{StaticResource CardBrush}" CornerRadius="6"
+                        <Border Background="{DynamicResource CardBrush}" CornerRadius="6"
-                                BorderBrush="{StaticResource BorderBrush}" BorderThickness="1"
+                                BorderBrush="{DynamicResource BorderBrush}" BorderThickness="1"
                                 Padding="14,12">
                             <Grid>
                                 <Grid.ColumnDefinitions>
@@ -161,16 +162,16 @@
                                 <StackPanel Grid.Column="1" VerticalAlignment="Center">
                                     <StackPanel Orientation="Horizontal">
                                         <TextBlock Text="ClaudeChecker" FontSize="12" FontWeight="SemiBold"
-                                                   Foreground="{StaticResource TextBrush}"/>
+                                                   Foreground="{DynamicResource TextBrush}"/>
                                         <Border Background="#F0F0F0" CornerRadius="3"
                                                 Margin="6,0,0,0" Padding="5,1">
                                             <TextBlock x:Name="VersionLabel" FontSize="11"
-                                                       Foreground="{StaticResource SecondaryBrush}"
+                                                       Foreground="{DynamicResource SecondaryBrush}"
                                                        FontFamily="Consolas"/>
                                         </Border>
                                     </StackPanel>
                                     <TextBlock Text="Built by superdooper86 &amp; claude"
-                                               FontSize="11" Foreground="{StaticResource SecondaryBrush}"/>
+                                               FontSize="11" Foreground="{DynamicResource SecondaryBrush}"/>
                                 </StackPanel>
                                 <Button Grid.Column="2" x:Name="CheckUpdateButton"
                                         Style="{StaticResource SmallButton}"
@@ -185,17 +186,17 @@
 
         <!-- Update panel -->
         <Border x:Name="UpdatePanel" Visibility="Collapsed"
-                Background="{StaticResource BackgroundBrush}">
+                Background="{DynamicResource BackgroundBrush}">
             <DockPanel>
-                <Border DockPanel.Dock="Top" BorderBrush="{StaticResource BorderBrush}"
+                <Border DockPanel.Dock="Top" BorderBrush="{DynamicResource BorderBrush}"
-                        BorderThickness="0,0,0,1" Background="#FAFAFA" Padding="12,10">
+                        BorderThickness="0,0,0,1" Background="{DynamicResource SurfaceBrush}" Padding="12,10">
                     <Grid>
                         <Button Content="← Back" HorizontalAlignment="Left"
                                 Style="{StaticResource SmallButton}" BorderThickness="0"
-                                Foreground="{StaticResource BlueBrush}" Background="Transparent"
+                                Foreground="{DynamicResource BlueBrush}" Background="Transparent"
                                 Click="CloseUpdate_Click"/>
                         <TextBlock Text="Update Available" FontSize="14" FontWeight="SemiBold"
-                                   Foreground="{StaticResource TextBrush}"
+                                   Foreground="{DynamicResource TextBrush}"
                                    HorizontalAlignment="Center" VerticalAlignment="Center"/>
                         <Button x:Name="NotNowButton" Content="Not Now" HorizontalAlignment="Right"
                                 Style="{StaticResource SmallButton}" Click="CloseUpdate_Click"/>
@@ -203,8 +204,8 @@
                 </Border>
 
                 <StackPanel Margin="20,16">
-                    <Border Background="{StaticResource CardBrush}" CornerRadius="6"
+                    <Border Background="{DynamicResource CardBrush}" CornerRadius="6"
-                            BorderBrush="{StaticResource BorderBrush}" BorderThickness="1"
+                            BorderBrush="{DynamicResource BorderBrush}" BorderThickness="1"
                             Padding="14,12" Margin="0,0,0,12">
                         <Grid>
                             <Grid.ColumnDefinitions>
@@ -216,26 +217,26 @@
                             <StackPanel Grid.Column="1" VerticalAlignment="Center">
                                 <StackPanel Orientation="Horizontal" Margin="0,0,0,4">
                                     <TextBlock x:Name="CurrentVerLabel" FontSize="12" FontFamily="Consolas"
-                                               Foreground="{StaticResource SecondaryBrush}" VerticalAlignment="Center"/>
+                                               Foreground="{DynamicResource SecondaryBrush}" VerticalAlignment="Center"/>
-                                    <TextBlock Text=" → " FontSize="11" Foreground="{StaticResource SecondaryBrush}"
+                                    <TextBlock Text=" → " FontSize="11" Foreground="{DynamicResource SecondaryBrush}"
                                                VerticalAlignment="Center"/>
                                     <TextBlock x:Name="NewVerLabel" FontSize="13" FontWeight="SemiBold"
-                                               FontFamily="Consolas" Foreground="{StaticResource BlueBrush}"
+                                               FontFamily="Consolas" Foreground="{DynamicResource BlueBrush}"
                                                VerticalAlignment="Center"/>
                                 </StackPanel>
                                 <TextBlock x:Name="ReleaseNotesText" FontSize="11" TextWrapping="Wrap"
-                                           Foreground="{StaticResource SecondaryBrush}" MaxHeight="160"/>
+                                           Foreground="{DynamicResource SecondaryBrush}" MaxHeight="160"/>
                             </StackPanel>
                         </Grid>
                     </Border>
 
-                    <TextBlock x:Name="UpdateStatusText" Foreground="{StaticResource SecondaryBrush}"
+                    <TextBlock x:Name="UpdateStatusText" Foreground="{DynamicResource SecondaryBrush}"
                                FontSize="11" TextWrapping="Wrap" TextAlignment="Center"
                                Visibility="Collapsed" Margin="0,0,0,8"/>
                     <ProgressBar x:Name="UpdateProgress" Visibility="Collapsed"
-                                 Height="4" Margin="0,0,0,12" Foreground="{StaticResource BlueBrush}"/>
+                                 Height="4" Margin="0,0,0,12" Foreground="{DynamicResource BlueBrush}"/>
                     <TextBlock Text="ClaudeChecker will download, replace itself, and relaunch automatically."
-                               FontSize="11" Foreground="{StaticResource SecondaryBrush}"
+                               FontSize="11" Foreground="{DynamicResource SecondaryBrush}"
                                TextWrapping="Wrap" TextAlignment="Center" Margin="0,0,0,12"/>
                     <Button x:Name="InstallButton" Content="⬇  Download &amp; Install"
                             Style="{StaticResource PrimaryButton}" HorizontalAlignment="Stretch"

windows/PopupWindow.xaml.cs

@@ -1,7 +1,9 @@
 using ClaudeCheckerWindows.Controls;
 using System;
+using System.Runtime.InteropServices;
 using System.Windows;
 using System.Windows.Controls;
+using System.Windows.Interop;
 using System.Windows.Media;
 using System.Windows.Threading;
 
@@ -14,6 +16,17 @@ public partial class PopupWindow : Window
     private readonly DispatcherTimer _clockTimer;
     private bool _dialogOpen;
 
+    [DllImport("dwmapi.dll")]
+    private static extern int DwmSetWindowAttribute(IntPtr hwnd, int attr, ref int value, int size);
+
+    private void ApplyTitleBarTheme()
+    {
+        var hwnd = new WindowInteropHelper(this).Handle;
+        if (hwnd == IntPtr.Zero) return;
+        int dark = ThemeManager.IsDark ? 1 : 0;
+        DwmSetWindowAttribute(hwnd, 20, ref dark, sizeof(int));
+    }
+
     public PopupWindow()
     {
         InitializeComponent();
@@ -31,6 +44,8 @@ public partial class PopupWindow : Window
         UpdateFooter();
 
         Closing += (_, e) => { e.Cancel = true; Hide(); };
+        SourceInitialized += (_, _) => ApplyTitleBarTheme();
+        ThemeManager.ThemeChanged += () => { ApplyTitleBarTheme(); RebuildCards(); };
     }
 
     // ── Card rendering ───────────────────────────────────────────────

windows/RELEASE_NOTES.md

@@ -1,3 +1,6 @@
-## What's new
+## What's new in beta.18
 
-Initial Windows release.
+- Fixed startup crash caused by frozen WPF brushes
+- Added system dark/light theme support (auto-detected, updates every 5 seconds)
+- Native centered window instead of menubar popup
+- Update notifications now work correctly for pre-release builds

windows/ThemeManager.cs

@@ -0,0 +1,77 @@
+using Microsoft.Win32;
+using System;
+using System.Windows;
+using System.Windows.Media;
+using System.Windows.Threading;
+
+namespace ClaudeCheckerWindows;
+
+public static class ThemeManager
+{
+    public static bool IsDark { get; private set; }
+    public static event Action? ThemeChanged;
+
+    public static void Initialize()
+    {
+        IsDark = ReadIsDark();
+        Apply();
+
+        var timer = new DispatcherTimer { Interval = TimeSpan.FromSeconds(5) };
+        timer.Tick += (_, _) =>
+        {
+            var nowDark = ReadIsDark();
+            if (nowDark == IsDark) return;
+            IsDark = nowDark;
+            Apply();
+            ThemeChanged?.Invoke();
+        };
+        timer.Start();
+    }
+
+    private static bool ReadIsDark()
+    {
+        try
+        {
+            using var key = Registry.CurrentUser.OpenSubKey(
+                @"Software\Microsoft\Windows\CurrentVersion\Themes\Personalize");
+            return (int)(key?.GetValue("AppsUseLightTheme") ?? 1) == 0;
+        }
+        catch { return false; }
+    }
+
+    private static void Apply()
+    {
+        var res = Application.Current.Resources;
+        if (IsDark)
+        {
+            Set(res, "BackgroundBrush",   Color.FromRgb(0x1C, 0x1C, 0x1E));
+            Set(res, "CardBrush",         Color.FromRgb(0x2C, 0x2C, 0x2E));
+            Set(res, "TextBrush",         Color.FromRgb(0xF5, 0xF5, 0xF5));
+            Set(res, "SecondaryBrush",    Color.FromRgb(0x8A, 0x8A, 0x8E));
+            Set(res, "BorderBrush",       Color.FromRgb(0x3A, 0x3A, 0x3C));
+            Set(res, "BlueBrush",         Color.FromRgb(0x3B, 0x82, 0xF6));
+            Set(res, "ButtonBrush",       Color.FromRgb(0x3A, 0x3A, 0x3C));
+            Set(res, "SurfaceBrush",      Color.FromRgb(0x25, 0x25, 0x27));
+            Set(res, "BannerBgBrush",     Color.FromRgb(0x1A, 0x31, 0x52));
+            Set(res, "BannerBorderBrush", Color.FromRgb(0x2A, 0x4A, 0x72));
+        }
+        else
+        {
+            Set(res, "BackgroundBrush",   Color.FromRgb(0xF3, 0xF3, 0xF3));
+            Set(res, "CardBrush",         Colors.White);
+            Set(res, "TextBrush",         Color.FromRgb(0x1C, 0x1C, 0x1C));
+            Set(res, "SecondaryBrush",    Color.FromRgb(0x6E, 0x6E, 0x6E));
+            Set(res, "BorderBrush",       Color.FromRgb(0xE0, 0xE0, 0xE0));
+            Set(res, "BlueBrush",         Color.FromRgb(0x00, 0x78, 0xD4));
+            Set(res, "ButtonBrush",       Colors.White);
+            Set(res, "SurfaceBrush",      Color.FromRgb(0xFA, 0xFA, 0xFA));
+            Set(res, "BannerBgBrush",     Color.FromRgb(0xE8, 0xF2, 0xFB));
+            Set(res, "BannerBorderBrush", Color.FromRgb(0xB3, 0xD6, 0xF5));
+        }
+    }
+
+    private static void Set(ResourceDictionary res, string key, Color color)
+    {
+        res[key] = new SolidColorBrush(color);
+    }
+}

windows/UpdateManager.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Diagnostics;
+using System.Reflection;
 using System.IO;
 using System.IO.Compression;
 using System.Net.Http;
@@ -55,7 +56,11 @@ public class UpdateManager : INotifyPropertyChanged
 
     public string CurrentVersion =>
         System.Reflection.Assembly.GetExecutingAssembly()
-              .GetName().Version?.ToString(3) ?? "1.0.0";
+              .GetCustomAttribute<System.Reflection.AssemblyInformationalVersionAttribute>()
+              ?.InformationalVersion.Split('+')[0]
+              ?? "1.0.0";
+
+    private bool IsPreReleaseBuild => CurrentVersion.Contains('-');
 
     public UpdateManager()
     {
@@ -91,7 +96,8 @@ public class UpdateManager : INotifyPropertyChanged
                 LatestBetaVersion = beta.Version;
                 BetaAvailable     = true;
 
-                if (BetaChannel && IsNewer(beta.Version, LatestVersion))
+                // Show beta update if user opted in, or if they're already running a beta
+                if ((BetaChannel || IsPreReleaseBuild) && IsNewer(beta.Version, LatestVersion))
                 {
                     LatestVersion   = beta.Version;
                     ReleaseNotes    = beta.Notes ?? "";