refactor(ui): migrate UnfinishedPlanningModal to ModalShell

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

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

@@ -1,5 +1,4 @@
 using Avalonia.Controls;
-using Avalonia.Input;
 
 namespace ClaudeDo.Ui.Views.Modals;
 
@@ -14,10 +13,4 @@ public partial class UnfinishedPlanningModalView : Window
                 vm.CloseAction = () => Close();
         };
     }
-
-    private void TitleBar_PointerPressed(object? sender, PointerPressedEventArgs e)
-    {
-        if (e.GetCurrentPoint(this).Properties.IsLeftButtonPressed)
-            BeginMoveDrag(e);
-    }
 }