feat: agent updates from SAC, poll config, SSH/WinRM fallback (0.12.0)

Add agent update settings, pending self-update via poll, desired config per host, and automatic or manual SSH/WinRM fallback when agents do not report agent.update events.

backend/app/jobs/host_silence_background.py

@@ -36,6 +36,9 @@ def _run_scan_once() -> None:
     try:
         results = run_host_silence_scan(db)
         notified = dispatch_host_silence_notifications(db, results)
+        from app.services.agent_update import process_agent_update_fallbacks
+
+        fallback_results = process_agent_update_fallbacks(db)
         db.commit()
         if results:
             logger.info(
@@ -44,6 +47,12 @@ def _run_scan_once() -> None:
                 sum(1 for r in results if r.created),
                 notified,
             )
+        if fallback_results:
+            logger.info(
+                "agent_update fallback: processed=%s ok=%s",
+                len(fallback_results),
+                sum(1 for r in fallback_results if r.get("ok")),
+            )
     except Exception:
         db.rollback()
         raise