… inspect)

Adds three read-only endpoints to the kanban dashboard plugin so the
SwitchUI workspace (and any other dashboard consumer) can track
workers across tasks without N+1 round-trips through /tasks/{task_id}.

- GET /workers/active
  Single SQL JOIN of task_runs + tasks where ended_at IS NULL,
  worker_pid IS NOT NULL, status='running'. Returns
  {workers: [...], count, checked_at}.

- GET /runs/{run_id}
  Direct lookup of any task_run row by id. Reuses existing
  kanban_db.get_run() helper and _run_dict() serialiser. 404 when
  not found. Mirrors GET /tasks/{task_id} 404 shape.

- GET /runs/{run_id}/inspect
  Live PID stats via psutil.Process.as_dict() — cpu_percent,
  memory_rss_bytes, memory_vms_bytes, num_threads, num_fds, status,
  create_time, cmdline. Short-circuits with alive:false when run
  has ended, has no worker_pid, the pid is gone, or psutil is
  unavailable. AccessDenied surfaces as alive:true with error
  rather than a 500.

11 new tests in tests/plugins/test_kanban_worker_runs.py cover the
empty-board case, running-task case, ended-run filtering,
missing-pid filtering, 404 paths, already-ended inspect, no-pid
inspect, dead-pid inspect, and live-pid inspect (psutil mocked).
All pass.

Companion termination endpoint (POST /runs/{run_id}/terminate) is
intentionally out of scope here — opening a separate issue first
since the RBAC and dispatcher-mediated soft-cancel design needs
maintainer input before code.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>