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/TodoDetailPage.xaml.cs

@@ -0,0 +1,91 @@
+// TodoDetailPage - View and edit a todo item
+
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Graphics;
+using Microsoft.Maui.Platform;
+
+namespace TodoApp;
+
+public partial class TodoDetailPage : ContentPage
+{
+    private readonly TodoItem _todo;
+    private readonly TodoService _service = TodoService.Instance;
+
+    // Colors for status label
+    private static readonly Color AccentColor = Color.FromArgb("#26A69A");
+    private static readonly Color TextPrimary = Color.FromArgb("#212121");
+
+    public TodoDetailPage(TodoItem todo)
+    {
+        try
+        {
+            Console.WriteLine($"[TodoDetailPage] Constructor starting for: {todo.Title}");
+            InitializeComponent();
+            Console.WriteLine($"[TodoDetailPage] InitializeComponent complete");
+
+            _todo = todo;
+
+            // Populate fields
+            Console.WriteLine($"[TodoDetailPage] Setting TitleEntry.Text");
+            TitleEntry.Text = _todo.Title;
+            Console.WriteLine($"[TodoDetailPage] Setting NotesEditor.Text");
+            NotesEditor.Text = _todo.Notes;
+            Console.WriteLine($"[TodoDetailPage] Setting CompletedCheckBox.IsChecked");
+            CompletedCheckBox.IsChecked = _todo.IsCompleted;
+            Console.WriteLine($"[TodoDetailPage] Calling UpdateStatusLabel");
+            UpdateStatusLabel(_todo.IsCompleted);
+            Console.WriteLine($"[TodoDetailPage] Setting CreatedLabel.Text");
+            CreatedLabel.Text = $"Created {_todo.CreatedAt:MMMM d, yyyy} at {_todo.CreatedAt:h:mm tt}";
+            Console.WriteLine($"[TodoDetailPage] Constructor complete");
+        }
+        catch (Exception ex)
+        {
+            Console.WriteLine($"[TodoDetailPage] EXCEPTION in constructor: {ex.GetType().Name}: {ex.Message}");
+            Console.WriteLine($"[TodoDetailPage] Stack trace: {ex.StackTrace}");
+            throw;
+        }
+    }
+
+    private void OnCompletedChanged(object? sender, Microsoft.Maui.Controls.CheckedChangedEventArgs e)
+    {
+        Console.WriteLine($"[TodoDetailPage] OnCompletedChanged: {e.Value}");
+        UpdateStatusLabel(e.Value);
+    }
+
+    private void UpdateStatusLabel(bool isCompleted)
+    {
+        if (StatusLabel == null)
+        {
+            Console.WriteLine($"[TodoDetailPage] UpdateStatusLabel: StatusLabel is null, skipping");
+            return;
+        }
+        Console.WriteLine($"[TodoDetailPage] UpdateStatusLabel: setting to {(isCompleted ? "Completed" : "In Progress")}");
+        StatusLabel.Text = isCompleted ? "Completed" : "In Progress";
+        StatusLabel.TextColor = isCompleted ? AccentColor : TextPrimary;
+    }
+
+    private async void OnSaveClicked(object? sender, EventArgs e)
+    {
+        _todo.Title = TitleEntry.Text ?? "";
+        _todo.Notes = NotesEditor.Text ?? "";
+        _todo.IsCompleted = CompletedCheckBox.IsChecked;
+
+        await Navigation.PopAsync();
+    }
+
+    private async void OnDeleteClicked(object? sender, EventArgs e)
+    {
+        // Show confirmation dialog
+        var confirmed = await LinuxDialogService.ShowAlertAsync(
+            "Delete Task",
+            $"Are you sure you want to delete \"{_todo.Title}\"? This action cannot be undone.",
+            "Delete",
+            "Cancel");
+
+        if (confirmed)
+        {
+            _service.DeleteTodo(_todo);
+            await Navigation.PopAsync();
+        }
+    }
+}