Initial samples: TodoApp and ShellDemo

Two sample applications demonstrating OpenMaui Linux:

TodoApp:
- Full task manager with NavigationPage
- CollectionView with XAML data binding
- DisplayAlert dialogs
- Grid layouts with star sizing

ShellDemo:
- Comprehensive control showcase
- Shell with flyout navigation
- All core MAUI controls demonstrated
- Real-time event logging

Both samples reference OpenMaui.Controls.Linux via NuGet.

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

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

TodoApp/TodoItem.cs

@@ -0,0 +1,81 @@
+// TodoItem - Data model for a todo item
+
+using System.ComponentModel;
+
+namespace TodoApp;
+
+public class TodoItem : INotifyPropertyChanged
+{
+    private string _title = "";
+    private string _notes = "";
+    private bool _isCompleted;
+    private DateTime _dueDate;
+
+    public int Id { get; set; }
+
+    /// <summary>
+    /// Index in the collection for alternating row colors.
+    /// </summary>
+    public int Index { get; set; }
+
+    public string Title
+    {
+        get => _title;
+        set
+        {
+            if (_title != value)
+            {
+                _title = value;
+                OnPropertyChanged(nameof(Title));
+            }
+        }
+    }
+
+    public string Notes
+    {
+        get => _notes;
+        set
+        {
+            if (_notes != value)
+            {
+                _notes = value;
+                OnPropertyChanged(nameof(Notes));
+            }
+        }
+    }
+
+    public bool IsCompleted
+    {
+        get => _isCompleted;
+        set
+        {
+            if (_isCompleted != value)
+            {
+                _isCompleted = value;
+                OnPropertyChanged(nameof(IsCompleted));
+            }
+        }
+    }
+
+    public DateTime DueDate
+    {
+        get => _dueDate;
+        set
+        {
+            if (_dueDate != value)
+            {
+                _dueDate = value;
+                OnPropertyChanged(nameof(DueDate));
+            }
+        }
+    }
+
+    public DateTime CreatedAt { get; set; } = DateTime.Now;
+
+    public event PropertyChangedEventHandler? PropertyChanged;
+
+    protected void OnPropertyChanged(string propertyName)
+    {
+        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+    }
+}