refactor(ui): harden context menu event handling and simplify bindings

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ClaudeDo.Ui/Views/MainWindow.axaml.cs

@@ -35,6 +35,7 @@ public partial class MainWindow : Window
             && DataContext is MainWindowViewModel vm)
         {
             vm.SelectedList = item;
+            e.Handled = true;
         }
     }
 }