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/TodoDetailPage.xaml.cs

@@ -0,0 +1,42 @@
+using System;
+using Microsoft.Maui.Controls;
+
+namespace TodoApp;
+
+public partial class TodoDetailPage : ContentPage
+{
+    private readonly TodoService _service = TodoService.Instance;
+    private readonly TodoItem _item;
+
+    public TodoDetailPage(TodoItem item)
+    {
+        InitializeComponent();
+        _item = item;
+
+        TitleEntry.Text = item.Title;
+        NotesEditor.Text = item.Notes;
+        CompletedCheckBox.IsChecked = item.IsCompleted;
+        CreatedLabel.Text = $"Created {item.CreatedAt:MMMM d, yyyy} at {item.CreatedAt:h:mm tt}";
+    }
+
+    private async void OnSaveClicked(object? sender, EventArgs e)
+    {
+        _item.Title = TitleEntry.Text ?? "";
+        _item.Notes = NotesEditor.Text ?? "";
+        _item.IsCompleted = CompletedCheckBox.IsChecked;
+        await Navigation.PopAsync();
+    }
+
+    private async void OnDeleteClicked(object? sender, EventArgs e)
+    {
+        bool confirm = await DisplayAlert("Delete Task",
+            "Are you sure you want to delete this task?",
+            "Delete", "Cancel");
+
+        if (confirm)
+        {
+            _service.RemoveTodo(_item);
+            await Navigation.PopAsync();
+        }
+    }
+}