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>

samples/TodoApp/TodoService.cs

@@ -0,0 +1,61 @@
+// TodoService - Manages todo items
+
+using System.Collections.ObjectModel;
+
+namespace TodoApp;
+
+public class TodoService
+{
+    private static TodoService? _instance;
+    public static TodoService Instance => _instance ??= new TodoService();
+
+    private int _nextId = 1;
+
+    public ObservableCollection<TodoItem> Todos { get; } = new();
+
+    private TodoService()
+    {
+        // Add sample todos with varying lengths to test MaxLines=2 with ellipsis
+        AddTodo("Learn OpenMaui Linux", "Explore the SkiaSharp-based rendering engine for .NET MAUI on Linux desktop. This is a very long description that should wrap to multiple lines and demonstrate the ellipsis truncation feature when MaxLines is set to 2.");
+        AddTodo("Build amazing apps", "Create cross-platform applications that run on Windows, macOS, iOS, Android, and Linux! With OpenMaui, you can write once and deploy everywhere.");
+        AddTodo("Share with the community", "Contribute to the open-source project and help others build great Linux apps. Join our growing community of developers who are passionate about bringing .NET MAUI to Linux.");
+    }
+
+    public TodoItem AddTodo(string title, string notes = "")
+    {
+        var todo = new TodoItem
+        {
+            Id = _nextId++,
+            Index = Todos.Count, // Set index for alternating row colors
+            Title = title,
+            Notes = notes,
+            DueDate = DateTime.Today.AddDays(7)
+        };
+        Todos.Add(todo);
+        return todo;
+    }
+
+    /// <summary>
+    /// Refreshes the Index property on all items for alternating row colors.
+    /// </summary>
+    public void RefreshIndexes()
+    {
+        for (int i = 0; i < Todos.Count; i++)
+        {
+            Todos[i].Index = i;
+        }
+    }
+
+    public TodoItem? GetTodo(int id)
+    {
+        return Todos.FirstOrDefault(t => t.Id == id);
+    }
+
+    public void DeleteTodo(TodoItem todo)
+    {
+        Todos.Remove(todo);
+    }
+
+    public int CompletedCount => Todos.Count(t => t.IsCompleted);
+    public int TotalCount => Todos.Count;
+}