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.Worker/Planning/PlanningChainCoordinator.cs

@@ -66,6 +66,24 @@ public sealed class PlanningChainCoordinator
         return sequenceable.Count;
     }
 
+    // User-triggered "send plan to queue". Only valid once the plan is finalized
+    // (children are "Planned"); otherwise the children are still drafts.
+    public async Task<int> QueuePlanAsync(string parentTaskId, CancellationToken ct = default)
+    {
+        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
+        var phase = await ctx.Tasks.AsNoTracking()
+            .Where(t => t.Id == parentTaskId)
+            .Select(t => (PlanningPhase?)t.PlanningPhase)
+            .FirstOrDefaultAsync(ct);
+
+        if (phase is null)
+            throw new InvalidOperationException($"Task {parentTaskId} not found.");
+        if (phase != PlanningPhase.Finalized)
+            throw new InvalidOperationException("Plan must be finalized before it can be queued.");
+
+        return await SetupChainAsync(parentTaskId, ct);
+    }
+
     public async Task<string?> OnChildFinishedAsync(
         string childTaskId, TaskStatus finalStatus, CancellationToken ct = default)
     {