ops: Loki/Alloy fleet enabled; Backrest+WAL-G+Gitea Gotify hooks; Immich WAL fix

- Alloy now active on CT 102, 103, 104, 109, 101, 105, 113, nuc (mix of
  Docker container + systemd binary); all hosts shipping journal/docker
  logs to Loki on CT 109. CT 103 alloy newly enabled.
- Backrest plans: actionGotify hooks on SUCCESS (prio 3) + ERROR/WARNING
  (prio 8). Gotify app 'Backrest', token AtIMGOYcZsb5HfO.
- WAL-G staleness monitor on CT 103 (hourly): pg_stat_archiver SSH/exec
  against CT 113 + CT 104 immich_postgres. Found Immich WAL push failing
  for 42h — root cause: garage container on bridge network not
  shared_backend (Garage 2026-05-28 incident aftermath). Reconnected to
  shared_backend; image pinned v0.9.4 in compose to match running.
- Gitea daily digest at 08:00 on PVE host nuc — yesterday's commits.
- Closes fkrebs/n8n-flows #2, #5, #6.

services-overview.md

@@ -67,6 +67,7 @@ Every service running in the homelab, with its access URL(s) and host. **Externa
 | Wetty (SSH-in-browser) | — | <http://192.168.1.8:4090> | CT 109 | — |
 | Backrest (backups UI) | — | <http://192.168.1.3:9898> | CT 103 | [[backrest-ct103]] |
 | Diun (image update notifier) | — | logs only (`docker logs diun`) | CT 109 | — |
+| Alloy (log/metric collector) | — | `:12345` (per host) | CT 104, 109, 102, 103, 101, 105, 113, nuc | — |
 
 ## Network / infra