Implement architecture improvements for 1.0 release

Priority 1 - Stability:
- Dirty region invalidation in SkiaRenderingEngine
- Font fallback chain (FontFallbackManager) for emoji/CJK/international text
- Input method polish with Fcitx5 support alongside IBus

Priority 2 - Platform Integration:
- Portal file picker (PortalFilePickerService) with zenity/kdialog fallback
- System theme detection (SystemThemeService) for GNOME/KDE/XFCE/etc
- Notification actions support with D-Bus callbacks

Priority 3 - Performance:
- GPU acceleration (GpuRenderingEngine) with OpenGL, software fallback
- Virtualization manager (VirtualizationManager) for list recycling

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Services/InputMethodServiceFactory.cs

@@ -45,6 +45,7 @@ public static class InputMethodServiceFactory
             return imePreference.ToLowerInvariant() switch
             {
                 "ibus" => CreateIBusService(),
+                "fcitx" or "fcitx5" => CreateFcitx5Service(),
                 "xim" => CreateXIMService(),
                 "none" => new NullInputMethodService(),
                 _ => CreateAutoService()
@@ -56,13 +57,30 @@ public static class InputMethodServiceFactory
 
     private static IInputMethodService CreateAutoService()
     {
-        // Try IBus first (most common on modern Linux)
+        // Check GTK_IM_MODULE for hint
+        var imModule = Environment.GetEnvironmentVariable("GTK_IM_MODULE")?.ToLowerInvariant();
+
+        // Try Fcitx5 first if it's the configured IM
+        if (imModule?.Contains("fcitx") == true && Fcitx5InputMethodService.IsAvailable())
+        {
+            Console.WriteLine("InputMethodServiceFactory: Using Fcitx5");
+            return CreateFcitx5Service();
+        }
+
+        // Try IBus (most common on modern Linux)
         if (IsIBusAvailable())
         {
             Console.WriteLine("InputMethodServiceFactory: Using IBus");
             return CreateIBusService();
         }
 
+        // Try Fcitx5 as fallback
+        if (Fcitx5InputMethodService.IsAvailable())
+        {
+            Console.WriteLine("InputMethodServiceFactory: Using Fcitx5");
+            return CreateFcitx5Service();
+        }
+
         // Fall back to XIM
         if (IsXIMAvailable())
         {
@@ -88,6 +106,19 @@ public static class InputMethodServiceFactory
         }
     }
 
+    private static IInputMethodService CreateFcitx5Service()
+    {
+        try
+        {
+            return new Fcitx5InputMethodService();
+        }
+        catch (Exception ex)
+        {
+            Console.WriteLine($"InputMethodServiceFactory: Failed to create Fcitx5 service - {ex.Message}");
+            return new NullInputMethodService();
+        }
+    }
+
     private static IInputMethodService CreateXIMService()
     {
         try