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/NewTodoPage.xaml.cs

@@ -0,0 +1,31 @@
+// NewTodoPage - Create a new todo item
+
+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();
+    }
+}