feat(ui): add reconcile tick to self-heal lost worker broadcasts

TasksIslandViewModel now runs a periodic tick that diffs the flat Items
collection against SQLite and patches properties in place (capped at 500
rows, sharing the Phase 1 delta sequence guard so it never overtakes a
fresher broadcast). Never rebuilds rows or triggers Regroup/LoadForList, so
it stays decoupled from the parallel Phase 2b virtualization work. The same
cadence now refreshes the long-lived Worktrees Overview, Log Visualizer, and
Merge Helper selection overlays; short-lived modals are untouched.

src/ClaudeDo.Ui/Views/WindowDialogService.cs

@@ -94,7 +94,11 @@ public sealed class WindowDialogService : IDialogService
     {
         var dlg = new MergeHelperSelectionModal { DataContext = vm };
         vm.CloseAction = () => dlg.Close();
-        dlg.Closed += (_, _) => vm.Result.TrySetResult(null);   // native close counts as cancel
+        dlg.Closed += (_, _) =>
+        {
+            vm.StopReconcileTick();
+            vm.Result.TrySetResult(null);   // native close counts as cancel
+        };
         await dlg.ShowDialog(_owner);
         return await vm.Result.Task;
     }