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>

Views/SkiaShell.cs

@@ -693,7 +693,7 @@ public class SkiaShell : SkiaLayoutView
         }
 
         SetCurrentContent(root.Content);
-        Title = root.Title;
+        Title = root.Title ?? string.Empty;
         Invalidate();
     }