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/TodoService.cs

@@ -0,0 +1,59 @@
+using System;
+using System.Collections.ObjectModel;
+using System.Linq;
+
+namespace TodoApp;
+
+public class TodoService
+{
+    private static TodoService? _instance;
+    public static TodoService Instance => _instance ??= new TodoService();
+
+    public ObservableCollection<TodoItem> Todos { get; } = new();
+
+    private int _nextId = 1;
+
+    private TodoService()
+    {
+        // Add sample data
+        AddTodo("Learn OpenMaui Linux",
+            "Explore the SkiaSharp-based rendering engine for .NET MAUI on Linux desktop. " +
+            "This is a very long description that should wrap to multiple lines and demonstrate " +
+            "the ellipsis truncation feature when MaxLines is set to 2.");
+        AddTodo("Build amazing apps",
+            "Create cross-platform applications that run on Windows, macOS, iOS, Android, and Linux! " +
+            "With OpenMaui, you can write once and deploy everywhere.");
+        AddTodo("Share with the community",
+            "Contribute to the open-source project and help others build great Linux apps. " +
+            "Join our growing community of developers who are passionate about bringing .NET MAUI to Linux.");
+    }
+
+    public void AddTodo(string title, string notes)
+    {
+        var todo = new TodoItem
+        {
+            Id = _nextId++,
+            Title = title,
+            Notes = notes,
+            Index = Todos.Count
+        };
+        Todos.Add(todo);
+    }
+
+    public void RemoveTodo(TodoItem item)
+    {
+        Todos.Remove(item);
+        RefreshIndexes();
+    }
+
+    public void RefreshIndexes()
+    {
+        for (int i = 0; i < Todos.Count; i++)
+        {
+            Todos[i].Index = i;
+        }
+    }
+
+    public int CompletedCount => Todos.Count(t => t.IsCompleted);
+    public int TotalCount => Todos.Count;
+}