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/NewTodoPage.xaml.cs

@@ -0,0 +1,29 @@
+using System;
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Graphics;
+
+namespace TodoApp;
+
+public partial class NewTodoPage : ContentPage
+{
+    private readonly TodoService _service = TodoService.Instance;
+
+    public NewTodoPage()
+    {
+        InitializeComponent();
+    }
+
+    private async void OnSaveClicked(object? sender, EventArgs e)
+    {
+        var title = TitleEntry.Text?.Trim();
+        if (string.IsNullOrEmpty(title))
+        {
+            TitleEntry.Placeholder = "Title is required!";
+            TitleEntry.PlaceholderColor = Colors.Red;
+            return;
+        }
+
+        _service.AddTodo(title, NotesEditor.Text ?? "");
+        await Navigation.PopAsync();
+    }
+}