feat(data): add Idle/Cancelled status, PlanningPhase enum, BlockedByTaskId field

Slice 1 of the worker-state-and-queue-consolidation refactor — additive only,
no caller changes. Introduces the new orthogonal status model:

- TaskStatus gains canonical Idle and Cancelled values; legacy values
  (Manual, Planning, Planned, Draft, Waiting) stay around until slice 6.
- New PlanningPhase enum (None/Active/Finalized) for parent tasks.
- New BlockedByTaskId FK on TaskEntity for sequential chain ordering;
  ON DELETE SET NULL so orphaned children become pickable.
- EF migration adds planning_phase and blocked_by_task_id columns plus
  the idx_tasks_blocked_by index. Also picks up an unrelated drift in
  app_settings.default_permission_mode that had been changed in code
  (commit 14cc9fb) without a migration.

src/ClaudeDo.Data/Models/TaskEntity.cs

@@ -2,17 +2,31 @@ namespace ClaudeDo.Data.Models;
 
 public enum TaskStatus
 {
-    Manual,
+    // Lifecycle (canonical values).
+    Idle,
     Queued,
     Running,
     Done,
     Failed,
+    Cancelled,
+
+    // Legacy values — kept for backwards compatibility while the worker
+    // layer is migrated to (Status, PlanningPhase, BlockedByTaskId).
+    // Removed in slice 6 of the worker-state-and-queue-consolidation refactor.
+    Manual,
     Planning,
     Planned,
     Draft,
     Waiting,
 }
 
+public enum PlanningPhase
+{
+    None,
+    Active,
+    Finalized,
+}
+
 public sealed class TaskEntity
 {
     public required string Id { get; init; }
@@ -20,6 +34,8 @@ public sealed class TaskEntity
     public required string Title { get; set; }
     public string? Description { get; set; }
     public TaskStatus Status { get; set; } = TaskStatus.Manual;
+    public PlanningPhase PlanningPhase { get; set; } = PlanningPhase.None;
+    public string? BlockedByTaskId { get; set; }
     public DateTime? ScheduledFor { get; set; }
     public string? Result { get; set; }
     public string? LogPath { get; set; }