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/ShellHandler.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using Microsoft.Maui.Controls;
 using Microsoft.Maui.Handlers;
 using Microsoft.Maui.Graphics;
 using SkiaSharp;
@@ -10,13 +11,13 @@ namespace Microsoft.Maui.Platform.Linux.Handlers;
 /// <summary>
 /// Handler for Shell on Linux using Skia rendering.
 /// </summary>
-public partial class ShellHandler : ViewHandler<IView, SkiaShell>
+public partial class ShellHandler : ViewHandler<Shell, SkiaShell>
 {
-    public static IPropertyMapper<IView, ShellHandler> Mapper = new PropertyMapper<IView, ShellHandler>(ViewHandler.ViewMapper)
+    public static IPropertyMapper<Shell, ShellHandler> Mapper = new PropertyMapper<Shell, ShellHandler>(ViewHandler.ViewMapper)
     {
     };
 
-    public static CommandMapper<IView, ShellHandler> CommandMapper = new(ViewHandler.ViewCommandMapper)
+    public static CommandMapper<Shell, ShellHandler> CommandMapper = new(ViewHandler.ViewCommandMapper)
     {
     };
 
@@ -39,12 +40,26 @@ public partial class ShellHandler : ViewHandler<IView, SkiaShell>
         base.ConnectHandler(platformView);
         platformView.FlyoutIsPresentedChanged += OnFlyoutIsPresentedChanged;
         platformView.Navigated += OnNavigated;
+
+        // Subscribe to Shell navigation events
+        if (VirtualView != null)
+        {
+            VirtualView.Navigating += OnShellNavigating;
+            VirtualView.Navigated += OnShellNavigated;
+        }
     }
 
     protected override void DisconnectHandler(SkiaShell platformView)
     {
         platformView.FlyoutIsPresentedChanged -= OnFlyoutIsPresentedChanged;
         platformView.Navigated -= OnNavigated;
+
+        if (VirtualView != null)
+        {
+            VirtualView.Navigating -= OnShellNavigating;
+            VirtualView.Navigated -= OnShellNavigated;
+        }
+
         base.DisconnectHandler(platformView);
     }
 
@@ -55,6 +70,24 @@ public partial class ShellHandler : ViewHandler<IView, SkiaShell>
 
     private void OnNavigated(object? sender, ShellNavigationEventArgs e)
     {
-        // Handle navigation events
+        // Handle platform navigation events
+    }
+
+    private void OnShellNavigating(object? sender, ShellNavigatingEventArgs e)
+    {
+        Console.WriteLine($"[ShellHandler] Shell Navigating to: {e.Target?.Location}");
+
+        // Route to platform view
+        if (PlatformView != null && e.Target?.Location != null)
+        {
+            var route = e.Target.Location.ToString().TrimStart('/');
+            Console.WriteLine($"[ShellHandler] Routing to: {route}");
+            PlatformView.GoToAsync(route);
+        }
+    }
+
+    private void OnShellNavigated(object? sender, ShellNavigatedEventArgs e)
+    {
+        Console.WriteLine($"[ShellHandler] Shell Navigated to: {e.Current?.Location}");
     }
 }