refactor(ui): migrate WorktreesOverviewModal to ModalShell

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

src/ClaudeDo.Ui/Views/Modals/WorktreesOverviewModalView.axaml.cs

@@ -17,9 +17,5 @@ public partial class WorktreesOverviewModalView : Window
         }
     }
 
-    private void OnTitleBarPressed(object? sender, PointerPressedEventArgs e)
-    {
-        if (e.GetCurrentPoint(this).Properties.IsLeftButtonPressed)
-            BeginMoveDrag(e);
-    }
+
 }