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/core/settings.py

@@ -57,6 +57,8 @@ DEFAULTS: dict[str, Any] = {
     "ansible.become_password": "",
     "ansible.vault_password": "",
     "ansible.host_key_checking": False,
+    # Max simultaneous playbook runs; extra runs queue. Applied at app start.
+    "ansible.max_concurrent_runs": 3,
     "ping.threshold.good_ms": 50,
     "ping.threshold.warn_ms": 200,
     "plugins.index_url": "https://git.fabledsword.com/bvandeusen/Steward-plugins/raw/branch/main/index.yaml",
@@ -175,6 +177,7 @@ def to_ansible_cfg(settings: dict[str, Any]) -> dict:
         "become_password": settings.get("ansible.become_password", ""),
         "vault_password": settings.get("ansible.vault_password", ""),
         "host_key_checking": settings.get("ansible.host_key_checking", False),
+        "max_concurrent_runs": settings.get("ansible.max_concurrent_runs", 3),
     }