feat(ansible): runner robustness — cancel, concurrency, structured results, retention

Closes #550 (all four):

- Cancellation: track live subprocesses; POST /ansible/runs/<id>/cancel
  (operator) SIGTERMs then SIGKILLs after a grace; new 'cancelled' status
  (+ migration 0019, ALTER TYPE in autocommit). Queued runs cancel cleanly
  before launch. Cancel button on run detail.
- Concurrency: global semaphore (ansible.max_concurrent_runs, default 3,
  Settings→Ansible) caps simultaneous runs; excess show 'queued' (new status)
  until a slot frees. Semaphore bound lazily per running loop.
- Structured results: parse PLAY RECAP into per-host ok/changed/unreachable/
  failed/skipped + capture failed-task lines, stored in new results JSON
  column (migration 0020); rendered as a host-summary table on run detail.
  Keeps live streaming (no json-callback swap).
- Retention: full output written to a persistent log artifact
  (/data/ansible/runs/<id>.log, env-overridable) beyond the 1 MB DB cap and
  across restarts; in-memory replay buffer bounded + GC'd after completion;
  Download-log route. Boot reconciliation now also sweeps stale 'queued'.

Unit tests for recap parsing + cancel flagging. Status colors updated across
run list / detail / schedules.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

steward/templates/ansible/index.html

@@ -27,7 +27,7 @@
     </thead>
     <tbody>
     {% for run in runs %}
-    {% set status_color = {"running": "var(--yellow)", "success": "var(--green)", "failed": "var(--red)", "interrupted": "var(--orange)"}.get(run.status.value, "var(--text-muted)") %}
+    {% set status_color = {"queued": "var(--text-dim)", "running": "var(--yellow)", "success": "var(--green)", "failed": "var(--red)", "interrupted": "var(--orange)", "cancelled": "var(--orange)"}.get(run.status.value, "var(--text-muted)") %}
     <tr>
         <td style="font-size:0.9rem;">{{ run.playbook_path }}</td>
         <td style="color:var(--text-muted);font-size:0.9rem;">{{ run.source_name }}</td>