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.
