refactor(data): retire legacy TaskStatus values and backfill existing rows

Slice 6 of the worker state and queue consolidation refactor.

* Drop Manual, Planning, Planned, Draft, Waiting from the TaskStatus enum
  and from the EF value converter; only the lifecycle values remain
  (Idle, Queued, Running, Done, Failed, Cancelled).
* Add migration RetireLegacyTaskStatus that rewrites existing rows:
  manual/draft -> idle, planning -> idle+planning_phase=active,
  planned -> idle+planning_phase=finalized, waiting -> queued+blocked_by
  derived from sort_order via a CTE with LAG().
* Reroute every call site that compared/set legacy values to the new
  three-field model (Status + PlanningPhase + BlockedByTaskId), including
  the planning repo helpers, MCP services, the planning chain coordinator,
  and the UI view-models. TaskRowViewModel now exposes PlanningPhase to
  drive the planning badge.
* Refresh Worker/CLAUDE.md and Data/CLAUDE.md, the docs/plan.md status
  section, and the planning verification notes in docs/open.md.

src/ClaudeDo.Data/Models/TaskEntity.cs

@@ -2,22 +2,12 @@ namespace ClaudeDo.Data.Models;
 
 public enum TaskStatus
 {
-    // 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
@@ -33,7 +23,7 @@ public sealed class TaskEntity
     public required string ListId { get; init; }
     public required string Title { get; set; }
     public string? Description { get; set; }
-    public TaskStatus Status { get; set; } = TaskStatus.Manual;
+    public TaskStatus Status { get; set; } = TaskStatus.Idle;
     public PlanningPhase PlanningPhase { get; set; } = PlanningPhase.None;
     public string? BlockedByTaskId { get; set; }
     public DateTime? ScheduledFor { get; set; }