Dispatcher.ShutdownStarted stack trace + fix log sink ordering

- Subscribe to Dispatcher.UIThread.ShutdownStarted in App.axaml.cs
  to capture the stack trace when the dispatcher dies (the actual cause)
- Move Logger.Sink assignment AFTER .LogToTrace() so it isn't overwritten
- This should finally reveal what crashes Avalonia on Linux

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bammf1

App.axaml.cs

@@ -34,6 +34,15 @@ public override void Initialize()
 
     public override void OnFrameworkInitializationCompleted()
     {
+        // Capture the exact moment the dispatcher shuts down — the stack trace
+        // reveals what code triggered it (the real crash, not the symptom).
+        Avalonia.Threading.Dispatcher.UIThread.ShutdownStarted += (_, _) =>
+        {
+            Console.Error.WriteLine("=== DISPATCHER SHUTDOWN STARTED ===");
+            Console.Error.WriteLine(Environment.StackTrace);
+            Console.Error.Flush();
+        };
+
         try
         {
             // Global CJK font for LiveCharts2 tooltips and labels.

Program.cs

@@ -77,14 +77,14 @@ public static void Main(string[] args)
     // Avalonia configuration, don't remove; also used by visual designer.
     public static AppBuilder BuildAvaloniaApp()
     {
-        // Log Avalonia internals to stderr so Linux crashes show the real cause
-        Avalonia.Logging.Logger.Sink = new StderrLogSink();
-
         var builder = AppBuilder.Configure<App>()
             .UsePlatformDetect()
             .WithInterFont()
             .LogToTrace();
 
+        // Set AFTER .LogToTrace() so our sink takes precedence (LogToTrace may overwrite)
+        Avalonia.Logging.Logger.Sink = new StderrLogSink();
+
         // On Linux, configure X11 with software rendering fallback and disable
         // DBus menu to avoid Wayland dispatcher shutdown crashes (Issue #19523).
         // Uses reflection because Avalonia.X11 types are only available at runtime