fix(ui): persist title edits from the detail pane

EditableTitle had no save handler at all (only EditableDescription did), so
retitling a task in the details island was silently discarded on rebind. Mirror
the debounced description save, capturing the row so a task switch mid-debounce
cannot retitle the wrong task.

src/ClaudeDo.Ui/ViewModels/Islands/DetailsIslandViewModel.cs

@@ -258,6 +258,9 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
     private bool _suppressDescSave;
     private CancellationTokenSource? _descSaveCts;
 
+    private bool _suppressTitleSave;
+    private CancellationTokenSource? _titleSaveCts;
+
     // Set by shell so CloseDetailCommand can clear SelectedTask
     public Action? CloseDetail { get; set; }
 
@@ -430,6 +433,39 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
         }
     }
 
+    partial void OnEditableTitleChanged(string value)
+    {
+        if (_suppressTitleSave || Task is null) return;
+        _titleSaveCts?.Cancel();
+        _titleSaveCts = new CancellationTokenSource();
+        // Capture the row so a task switch mid-debounce cannot retitle the new task.
+        _ = SaveTitleAsync(Task, value, _titleSaveCts.Token);
+    }
+
+    private async System.Threading.Tasks.Task SaveTitleAsync(
+        TaskRowViewModel row, string value, CancellationToken ct)
+    {
+        try
+        {
+            await System.Threading.Tasks.Task.Delay(400, ct);
+            var title = value?.Trim();
+            // An empty title would make the row unidentifiable — keep the stored one.
+            if (string.IsNullOrEmpty(title)) return;
+            await using var ctx = _dbFactory.CreateDbContext();
+            var repo = new TaskRepository(ctx);
+            var entity = await repo.GetByIdAsync(row.Id);
+            if (entity is null || entity.Title == title) return;
+            entity.Title = title;
+            await repo.UpdateAsync(entity);
+            ct.ThrowIfCancellationRequested();
+            row.Title = title;
+            if (ReferenceEquals(Task, row))
+                Merge.SyncTaskContext(row.Id, title, row.IsPlanningParent);
+        }
+        catch (OperationCanceledException) { }
+        catch { }
+    }
+
     partial void OnEditableDescriptionChanged(string value)
     {
         if (_suppressDescSave || Task is null) return;
@@ -525,7 +561,9 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase, IDisposable
             ct.ThrowIfCancellationRequested();
             if (entity == null) return;
 
-            EditableTitle = entity.Title;
+            _suppressTitleSave = true;
+            try { EditableTitle = entity.Title; }
+            finally { _suppressTitleSave = false; }
             _suppressDescSave = true;
             try { EditableDescription = entity.Description ?? ""; }
             finally { _suppressDescSave = false; }