feat(ui): always-visible Steps section at top of DetailsIsland with add-step input

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

@@ -110,6 +110,8 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase
     public ObservableCollection<LogLineViewModel> Log { get; } = new();
     public ObservableCollection<SubtaskRowViewModel> Subtasks { get; } = new();
 
+    [ObservableProperty] private string _newSubtaskTitle = "";
+
     // Claude CLI stream-json parser + buffer for partial text deltas
     private readonly StreamLineFormatter _formatter = new();
     private readonly StringBuilder _claudeBuf = new();
@@ -487,6 +489,30 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase
         CloseDetail?.Invoke();
     }
 
+    [RelayCommand]
+    private async System.Threading.Tasks.Task AddSubtaskAsync()
+    {
+        if (Task is null) return;
+        var title = NewSubtaskTitle?.Trim();
+        if (string.IsNullOrEmpty(title)) return;
+
+        var entity = new ClaudeDo.Data.Models.SubtaskEntity
+        {
+            Id = Guid.NewGuid().ToString(),
+            TaskId = Task.Id,
+            Title = title,
+            Completed = false,
+            OrderNum = Subtasks.Count,
+            CreatedAt = DateTime.UtcNow,
+        };
+
+        await using var ctx = _dbFactory.CreateDbContext();
+        await new SubtaskRepository(ctx).AddAsync(entity);
+
+        Subtasks.Add(new SubtaskRowViewModel { Id = entity.Id, Title = entity.Title, Done = entity.Completed });
+        NewSubtaskTitle = "";
+    }
+
     [RelayCommand]
     private async System.Threading.Tasks.Task SaveNotesAsync()
     {