feat(planning): gate subtask queueing behind plan finalization

Planning subtasks are now "Draft" until their parent plan is finalized,
then "Planned" (queueable). Finalizing a plan no longer auto-queues the
child chain; the user sends the plan to the queue explicitly.

- TaskStateService rejects a child entering Queued/Running unless its parent
  is Finalized; this single invariant covers UI, queue, RunNow and MCP paths
- WorkerHub.SetTaskStatus routes Queued through the gated EnqueueAsync
- Finalize call sites pass queueAgentTasks: false
- PlanningChainCoordinator.QueuePlanAsync guards the chain build on Finalized
- TaskRowViewModel derives Draft/Planned from ParentFinalized; gates
  CanSendToQueue / CanQueuePlan; view shows a PLANNED badge

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

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

@@ -853,7 +853,8 @@ public sealed partial class DetailsIslandViewModel : ViewModelBase
     }
 
     private bool CanEnqueue() =>
-        Task != null && _worker.IsConnected && IsIdle;
+        Task != null && _worker.IsConnected && IsIdle
+        && (!Task.IsChild || Task.ParentFinalized);
 
     [RelayCommand(CanExecute = nameof(CanDequeue))]
     private async System.Threading.Tasks.Task DequeueAsync()