Fix incomplete functionality, nullable warnings, and async issues

Incomplete functionality fixes:
- SkiaEditor: Wire up Completed event to fire on focus lost
- X11InputMethodService: Remove unused _commitCallback field
- SkiaWebView: Set _isProperlyReparented when reparenting succeeds,
  use _lastMainX/_lastMainY to track main window position,
  add _isEmbedded guard to prevent double embedding

Nullable reference fixes:
- Easing: Reorder BounceOut before BounceIn (static init order)
- GestureManager: Use local command variable instead of re-accessing
- SkiaShell: Handle null Title with ?? operator
- GLibNative: Use null! for closure pattern
- LinuxProgramHost: Default title if null
- SkiaWebView.LoadHtml: Add null/empty check for html
- SystemThemeService: Initialize Colors with default values
- DeviceDisplayService/AppInfoService: Use var for nullable env vars
- EmailService: Add null check for message parameter

Async fixes:
- SkiaImage: Use _ = for fire-and-forget async calls
- SystemTrayService: Convert async method without await to sync Task

Reduces warnings from 156 to 133 (remaining are P/Invoke structs
and obsolete MAUI API usage)

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

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

Services/SystemTrayService.cs

@@ -101,7 +101,7 @@ public class SystemTrayService : IDisposable
         _ = ShowAsync();
     }
 
-    private async Task<bool> TryYadTray()
+    private Task<bool> TryYadTray()
     {
         try
         {
@@ -118,7 +118,7 @@ public class SystemTrayService : IDisposable
             };
 
             _trayProcess = Process.Start(startInfo);
-            if (_trayProcess == null) return false;
+            if (_trayProcess == null) return Task.FromResult(false);
 
             // Start reading output for menu clicks
             _ = Task.Run(async () =>
@@ -137,11 +137,11 @@ public class SystemTrayService : IDisposable
                 catch { }
             });
 
-            return true;
+            return Task.FromResult(true);
         }
         catch
         {
-            return false;
+            return Task.FromResult(false);
         }
     }