Add TodoApp sample with reconstructed XAML

Complete TodoApp sample application with:
- App.xaml/cs: Colors and styles for light/dark themes
- TodoListPage: Task list with theme toggle switch
- NewTodoPage: Form to create new tasks
- TodoDetailPage: Edit task details with delete option
- TodoItem.cs/TodoService.cs: Data model and service
- SVG icons for save, delete, and add actions

Theme switching via toggle on main page applies app-wide.

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

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

samples/TodoApp/TodoListPage.xaml.cs

@@ -0,0 +1,69 @@
+using System;
+using Microsoft.Maui.ApplicationModel;
+using Microsoft.Maui.Controls;
+
+namespace TodoApp;
+
+public partial class TodoListPage : ContentPage
+{
+    private readonly TodoService _service = TodoService.Instance;
+    private bool _isNavigating;
+
+    public TodoListPage()
+    {
+        InitializeComponent();
+        TodoCollectionView.ItemsSource = _service.Todos;
+        UpdateStats();
+        ThemeSwitch.IsToggled = Application.Current?.UserAppTheme == AppTheme.Dark;
+    }
+
+    protected override void OnAppearing()
+    {
+        base.OnAppearing();
+        _isNavigating = false;
+        _service.RefreshIndexes();
+        TodoCollectionView.ItemsSource = null;
+        TodoCollectionView.ItemsSource = _service.Todos;
+        UpdateStats();
+    }
+
+    private void OnThemeToggled(object? sender, ToggledEventArgs e)
+    {
+        if (Application.Current != null)
+        {
+            Application.Current.UserAppTheme = e.Value ? AppTheme.Dark : AppTheme.Light;
+            // Refresh to apply theme
+            var items = TodoCollectionView.ItemsSource;
+            TodoCollectionView.ItemsSource = null;
+            TodoCollectionView.ItemsSource = items;
+        }
+    }
+
+    private async void OnAddClicked(object? sender, EventArgs e)
+    {
+        await Navigation.PushAsync(new NewTodoPage());
+    }
+
+    private async void OnItemTapped(object? sender, TappedEventArgs e)
+    {
+        if (_isNavigating || e.Parameter is not TodoItem todoItem)
+            return;
+
+        _isNavigating = true;
+        try
+        {
+            await Navigation.PushAsync(new TodoDetailPage(todoItem));
+        }
+        catch
+        {
+            _isNavigating = false;
+        }
+    }
+
+    private void UpdateStats()
+    {
+        int completed = _service.CompletedCount;
+        int total = _service.TotalCount;
+        StatsLabel.Text = total == 0 ? "" : $"Tasks: {completed} of {total}";
+    }
+}