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.
7b737e6717