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/SliderHandler.cs

@@ -22,6 +22,7 @@ public partial class SliderHandler : ViewHandler<ISlider, SkiaSlider>
         [nameof(ISlider.MaximumTrackColor)] = MapMaximumTrackColor,
         [nameof(ISlider.ThumbColor)] = MapThumbColor,
         [nameof(IView.Background)] = MapBackground,
+        [nameof(IView.IsEnabled)] = MapIsEnabled,
     };
 
     public static CommandMapper<ISlider, SliderHandler> CommandMapper = new(ViewHandler.ViewCommandMapper)
@@ -48,6 +49,15 @@ public partial class SliderHandler : ViewHandler<ISlider, SkiaSlider>
         platformView.ValueChanged += OnValueChanged;
         platformView.DragStarted += OnDragStarted;
         platformView.DragCompleted += OnDragCompleted;
+
+        // Sync properties that may have been set before handler connection
+        if (VirtualView != null)
+        {
+            MapMinimum(this, VirtualView);
+            MapMaximum(this, VirtualView);
+            MapValue(this, VirtualView);
+            MapIsEnabled(this, VirtualView);
+        }
     }
 
     protected override void DisconnectHandler(SkiaSlider platformView)
@@ -133,4 +143,11 @@ public partial class SliderHandler : ViewHandler<ISlider, SkiaSlider>
             handler.PlatformView.BackgroundColor = solidPaint.Color.ToSKColor();
         }
     }
+
+    public static void MapIsEnabled(SliderHandler handler, ISlider slider)
+    {
+        if (handler.PlatformView is null) return;
+        handler.PlatformView.IsEnabled = slider.IsEnabled;
+        handler.PlatformView.Invalidate();
+    }
 }