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/README.md

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+# NFS Self-Heal (host-level systemd units)
+
+These files are **not** deployed by Docker/Portainer — they're systemd units and a
+script that live directly on the host at `/etc/systemd/system/` and
+`/usr/local/bin/`. They're checked in here purely as a backup so they can be
+restored if the host is rebuilt. Editing a file here does **not** change
+running behavior; you have to re-copy it to the host and reload systemd.
+
+## What this does
+
+Permanent NFS mounts (`mnt-nas_family.mount`, `mnt-nas_books.mount`,
+`mnt-nas_owncloud.mount`) can go stale — the host mount looks fine on a
+top-level `ls`, but file handles nested inside it return ESTALE
+(errno -116) to processes that opened them earlier, including containers
+that bind-mount the path. A container restart is required to pick up a
+fresh handle even after the host-side mount is healthy again. See
+`../../NAS-CONNECTION-STRATEGIES.md` for the full mount inventory and
+`../../immich/` / `../../calibre/MOUNT-HISTORY.md` for history on this
+failure mode (first hit immich on 2026-08-25; calibre-import had the same
+issue documented earlier but unresolved).
+
+Two pieces:
+
+1. **`<container>-mount-ready.service`** (one per affected container) —
+   `BindsTo=mnt-nas_*.mount`, so restarting the mount unit automatically
+   restarts the bound container. Currently covers `immich_server`,
+   `calibre`, `ocis`. (Older instances of this same pattern —
+   `backrest`, `kiwix`, `pmtiles`, `audiobookshelf`, `romm` — already
+   exist on the host but aren't backed up here yet.)
+2. **`nfs-mount-heal.timer`** → **`nfs-mount-heal.service`** →
+   **`nfs-mount-heal.sh`** — runs every 5 minutes, does a real nested
+   read (not just `ls` the mount root) against `nas_family`, `nas_books`,
+   and `nas_owncloud`. On failure it force-remounts the mount unit
+   (`systemctl restart`), which cascades into the container restart via
+   the hooks above, then re-checks and sends a Telegram alert either way.
+
+## Reinstall after a host rebuild
+
+```bash
+sudo cp *.service *.timer /etc/systemd/system/
+sudo cp nfs-mount-heal.sh /usr/local/bin/nfs-mount-heal.sh
+sudo chmod 755 /usr/local/bin/nfs-mount-heal.sh
+
+sudo systemctl daemon-reload
+sudo systemctl enable --now immich-mount-ready.service
+sudo systemctl enable --now calibre-mount-ready.service
+sudo systemctl enable --now ocis-mount-ready.service
+sudo systemctl enable --now nfs-mount-heal.timer
+```
+
+Requires the `mnt-nas_family.mount`, `mnt-nas_books.mount`, and
+`mnt-nas_owncloud.mount` systemd units to already exist (see
+`NAS-CONNECTION-STRATEGIES.md`) and `.credentials` at the repo root to be
+present on the host (the heal script sources it for the Telegram bot
+token/chat ID).