Preview 3: Complete control implementation with XAML data binding

Major milestone adding full control functionality:

Controls Enhanced:
- Entry/Editor: Full keyboard input, cursor navigation, selection, clipboard
- CollectionView: Data binding, selection highlighting, scrolling
- CheckBox/Switch/Slider: Interactive state management
- Picker/DatePicker/TimePicker: Dropdown selection with popup overlays
- ProgressBar/ActivityIndicator: Animated progress display
- Button: Press/release visual states
- Border/Frame: Rounded corners, stroke styling
- Label: Text wrapping, alignment, decorations
- Grid/StackLayout: Margin and padding support

Features Added:
- DisplayAlert dialogs with button actions
- NavigationPage with toolbar and back navigation
- Shell with flyout menu navigation
- XAML value converters for data binding
- Margin support in all layout containers
- Popup overlay system for pickers

New Samples:
- TodoApp: Full CRUD task manager with NavigationPage
- ShellDemo: Comprehensive control showcase

Removed:
- ControlGallery (replaced by ShellDemo)
- LinuxDemo (replaced by TodoApp)

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

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

Handlers/EditorHandler.cs

@@ -31,6 +31,7 @@ public partial class EditorHandler : ViewHandler<IEditor, SkiaEditor>
             [nameof(IEditor.HorizontalTextAlignment)] = MapHorizontalTextAlignment,
             [nameof(IEditor.VerticalTextAlignment)] = MapVerticalTextAlignment,
             [nameof(IView.Background)] = MapBackground,
+            ["BackgroundColor"] = MapBackgroundColor,
         };
 
     public static CommandMapper<IEditor, EditorHandler> CommandMapper =
@@ -82,6 +83,7 @@ public partial class EditorHandler : ViewHandler<IEditor, SkiaEditor>
     {
         if (handler.PlatformView is null) return;
         handler.PlatformView.Text = editor.Text ?? "";
+        handler.PlatformView.Invalidate();
     }
 
     public static void MapPlaceholder(EditorHandler handler, IEditor editor)
@@ -165,4 +167,15 @@ public partial class EditorHandler : ViewHandler<IEditor, SkiaEditor>
             handler.PlatformView.BackgroundColor = solidPaint.Color.ToSKColor();
         }
     }
+
+    public static void MapBackgroundColor(EditorHandler handler, IEditor editor)
+    {
+        if (handler.PlatformView is null) return;
+
+        if (editor is VisualElement ve && ve.BackgroundColor != null)
+        {
+            handler.PlatformView.BackgroundColor = ve.BackgroundColor.ToSKColor();
+            handler.PlatformView.Invalidate();
+        }
+    }
 }