feat(ui): show dequeue affordance on planning parents with queued children

Planning parents stay in Planning/Planned status while their children are
Queued/Waiting, so the existing IsQueued-only visibility rule hid the dequeue
button. Add HasQueuedSubtasks tracking and a CanRemoveFromQueue helper; the
parent-row dequeue cascades to all queued/waiting children. Also attach the
'agent' tag on explicit enqueue so the queue picker accepts the task.

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

@@ -26,6 +26,7 @@ public sealed partial class TaskRowViewModel : ViewModelBase
     [ObservableProperty] private string? _parentTaskId;
     [ObservableProperty] private bool _isExpanded = true;
     [ObservableProperty] private bool _hasPlanningChildren;
+    [ObservableProperty] private bool _hasQueuedSubtasks;
 
     public DateTime CreatedAt { get; init; }
     public string CreatedAtFormatted => CreatedAt == default ? "—" : $"Created {CreatedAt:MMM d}";
@@ -58,6 +59,7 @@ public sealed partial class TaskRowViewModel : ViewModelBase
     public bool IsRunning   => Status == TaskStatus.Running;
     public bool IsQueued    => Status == TaskStatus.Queued;
     public bool IsWaiting   => Status == TaskStatus.Waiting;
+    public bool CanRemoveFromQueue => IsQueued || HasQueuedSubtasks;
     public bool HasSchedule => ScheduledFor.HasValue;
     public bool HasLiveTail => IsRunning && !string.IsNullOrEmpty(LiveTail);
 
@@ -87,8 +89,12 @@ public sealed partial class TaskRowViewModel : ViewModelBase
         OnPropertyChanged(nameof(IsDraft));
         OnPropertyChanged(nameof(CanOpenPlanningSession));
         OnPropertyChanged(nameof(CanResumeOrDiscardPlanning));
+        OnPropertyChanged(nameof(CanRemoveFromQueue));
     }
 
+    partial void OnHasQueuedSubtasksChanged(bool value)
+        => OnPropertyChanged(nameof(CanRemoveFromQueue));
+
     partial void OnParentTaskIdChanged(string? value)
     {
         OnPropertyChanged(nameof(IsChild));