feat(ui): open Mission Control from the title bar

src/ClaudeDo.App/App.axaml.cs

@@ -1,5 +1,6 @@
 using System;
 using Avalonia;
+using Avalonia.Controls;
 using Avalonia.Controls.ApplicationLifetimes;
 using Avalonia.Markup.Xaml;
 using ClaudeDo.Ui.Services;
@@ -32,6 +33,10 @@ public partial class App : Application
 
             FocusClearing.Install();
 
+            // The main window is authoritative — closing it shuts the app down even if the
+            // modeless Mission Control window is still open.
+            desktop.ShutdownMode = ShutdownMode.OnMainWindowClose;
+
             desktop.MainWindow = new MainWindow
             {
                 DataContext = services.GetRequiredService<IslandsShellViewModel>(),