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.Worker/Planning/PlanningMcpService.cs

@@ -49,7 +49,7 @@ public sealed class PlanningMcpService
         var child = await _tasks.CreateChildAsync(ctx.ParentTaskId, title, description, tags, commitType, cancellationToken);
         await BroadcastTaskUpdatedAsync(child.Id, cancellationToken);
         await BroadcastTaskUpdatedAsync(ctx.ParentTaskId, cancellationToken);
-        return new CreatedChildDto(child.Id, "Draft");
+        return new CreatedChildDto(child.Id, child.Status.ToString());
     }
 
     [McpServerTool, Description("List all child tasks under the current planning session's parent task.")]
@@ -68,9 +68,9 @@ public sealed class PlanningMcpService
     }
 
     private static readonly TaskStatus[] EditableStatuses =
-        { TaskStatus.Draft, TaskStatus.Idle, TaskStatus.Manual, TaskStatus.Queued };
+        { TaskStatus.Idle, TaskStatus.Queued };
 
-    [McpServerTool, Description("Update a child task in the active planning session. Can change title, description, tags (replaces the full set), commit type, and status. Status must be one of: Draft, Idle, Manual, Queued.")]
+    [McpServerTool, Description("Update a child task in the active planning session. Can change title, description, tags (replaces the full set), commit type, and status. Status must be one of: Idle, Queued.")]
     public async Task<ChildTaskDto> UpdateChildTask(
         string taskId,
         string? title,
@@ -97,7 +97,7 @@ public sealed class PlanningMcpService
             if (!Enum.TryParse<TaskStatus>(status, ignoreCase: true, out var parsed))
                 throw new InvalidOperationException($"Unknown status '{status}'.");
             if (!EditableStatuses.Contains(parsed))
-                throw new InvalidOperationException($"Status '{parsed}' cannot be set via MCP. Allowed: Draft, Idle, Manual, Queued.");
+                throw new InvalidOperationException($"Status '{parsed}' cannot be set via MCP. Allowed: Idle, Queued.");
             newStatus = parsed;
         }