Closes the termination-control gap left by PR #28432, which shipped the
read-only sibling endpoints (/workers/active, /runs/{run_id},
/runs/{run_id}/inspect) but no way to stop a misbehaving worker from
the dashboard without dropping to the CLI.
The new endpoint resolves run_id -> task_id and delegates to the
existing kanban_db.reclaim_task() flow, so the SIGTERM->SIGKILL
escalation, run-outcome bookkeeping, and event-log append all match
POST /tasks/{task_id}/reclaim exactly. No new termination semantics
introduced.
Responses:
200 {ok, run_id, task_id} on success
404 unknown run_id
409 run already ended OR task no longer reclaimable
Refs: #23762
9d4fda9952