fix(host_agent): the maintenance-jobs migration waits for maintenance_windows, and the guards know the new table and action (#5767)

CI 9146 on 22b0be2:
- integration: host_agent_007 ran before core 0010 created maintenance_windows
  (its window_id foreign key), so the schema never built. It now
  depends_on 0010_maintenance_windows.
- unit: host_maintenance_jobs is named in the backup's EXCLUDED (run
  history, like ansible_runs and host_downtime), and the
  host_agent.maintenance audit action has its wording.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

steward/audit/service.py

@@ -137,6 +137,7 @@ ACTIONS = {
     "user.joined": "joined from an invite as",
     "host.created": "added host",
     "host.renamed": "renamed host",
+    "host_agent.maintenance": "started maintenance (update, reboot if needed) on host",
     "host.deleted": "deleted host",
     "monitor.created": "added monitor",
     "monitor.updated": "changed monitor",