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/Views/Islands/TaskRowView.axaml

@@ -60,7 +60,7 @@
                       IsVisible="{Binding CanResumeOrDiscardPlanning}"/>
             <MenuItem Header="Queue subtasks sequentially"
                       Click="OnQueuePlanningSubtasksClick"
-                      IsVisible="{Binding HasPlanningChildren}"/>
+                      IsVisible="{Binding CanQueuePlan}"/>
             <Separator/>
             <MenuItem Header="Schedule for..." Click="OnScheduleForClick"/>
             <MenuItem Header="Clear schedule"
@@ -113,6 +113,9 @@
               <Border Classes="badge draft" IsVisible="{Binding IsDraft}">
                 <TextBlock Text="DRAFT"/>
               </Border>
+              <Border Classes="badge planning" IsVisible="{Binding IsPlanned}">
+                <TextBlock Text="PLANNED"/>
+              </Border>
               <Border Classes="badge planning" IsVisible="{Binding IsPlanningParent}">
                 <TextBlock Text="{Binding PlanningBadge}"/>
               </Border>