docs(kanban): document POST /runs/{run_id}/terminate worker-terminate endpoint (#34449)

[r266-tech]

#34449 added a kanban REST control endpoint to terminate a live worker run — plugins/kanban/dashboard/plugin_api.py: @router.post("/runs/{run_id}/terminate") (TerminateRunBody), routing through kanban_db.reclaim_task (SIGTERM→SIGKILL + run-outcome bookkeeping + event-log append), returning {"ok": true, "run_id": ..., "task_id": ...} (404 unknown run / 409 already-ended). Its own docstring notes it "closes the gap left by PR #28432, which shipped the read-only sibling endpoints but no termination control surface."

The Worker visibility endpoints section only documented the three read-only GET endpoints. This adds the terminate control to the table (kept distinct from the read-only set) and updates the surrounding prose. Pure docs.

[teknium1]

Thanks for documenting the worker-termination control surface.

This is an automated hermes-sweeper review: current main already documents the endpoint, so this docs-only PR is redundant.

• website/docs/user-guide/features/kanban.md:720 lists POST /api/plugins/kanban/runs/{run_id}/terminate and describes its worker-stop/re-dispatch behavior.
• Commit 2d099fed1e0331d0800d3cada4f5a89102fc8a8d (docs: deep audit — registry drift, stale claims, 2-week PR coverage, dashboard screenshot (#40952)) added the current documentation and is an ancestor of main.
• The documented route matches the live handler at plugins/kanban/dashboard/plugin_api.py:1507.