Add NFS self-heal automation for immich/calibre/ocis, backed up in git

Stale NFS handles inside containers (ESTALE/errno -116) can persist even
after the host-side mount looks healthy, requiring a manual remount +
container restart. Adds systemd mount-ready hooks (BindsTo) to restart
immich_server/calibre/ocis when their NFS mount unit restarts, plus a
5-minute health-check timer that does a real nested read and force-remounts
on staleness. Host files backed up under system-config/nfs-self-heal/ so
they can be reinstalled after a host rebuild.

system-config/nfs-self-heal/nfs-mount-heal.timer

@@ -0,0 +1,9 @@
+[Unit]
+Description=Run NFS mount self-heal check every 5 minutes
+
+[Timer]
+OnBootSec=5min
+OnUnitActiveSec=5min
+
+[Install]
+WantedBy=timers.target