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/MauiProgram.cs

@@ -0,0 +1,24 @@
+using Microsoft.Maui;
+using Microsoft.Maui.Controls.Hosting;
+using Microsoft.Maui.Hosting;
+using Microsoft.Maui.Platform.Linux.Hosting;
+
+namespace TodoApp;
+
+public static class MauiProgram
+{
+    public static MauiApp CreateMauiApp()
+    {
+        var builder = MauiApp.CreateBuilder();
+        builder
+            .UseMauiApp<App>()
+            .UseLinuxPlatform()
+            .ConfigureFonts(fonts =>
+            {
+                fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
+                fonts.AddFont("OpenSans-Semibold.ttf", "OpenSansSemibold");
+            });
+
+        return builder.Build();
+    }
+}