feat(media): share one metadata set between Jellyfin and Plex over an SSD overlay

Both media servers read a Kodi-format sidecar (movie.nfo / tvshow.nfo /
episode.nfo) only when it sits next to the media file, and the library lives on
the RAID6 array, deliberately mounted read-only for every container and slow to
seek for a thousand tiny XML reads. So neither server binds the array any more:
both bind /mnt/media, an OverlayFS merge of the array (lowerdir, never written)
with /var/lib/media-meta on the NVMe (upperdir, where every write lands).

Jellyfin binds the view rw at /data and is the fleet's only metadata writer;
Plex binds it ro at /mnt/entropy, the container path its own database already
recorded, so only the host side of that bind moved and its library paths keep
resolving.

scripts/media-view.sh plans, installs, verifies, reports and reaps the view. It
refuses to mount over an unmounted array, refuses an upper layer on rotational
storage, and refuses a non-root install. deploy-remote.sh raises the view before
it restarts either media server, both units carry
ConditionPathIsMountPoint=/mnt/media so a missing view skips the start instead of
letting a scan clear the library database, and the planner routes the installer
and dankserver/host/** to the jellyfin+plex pair.

tests/media_overlay.bats (11 seams) pins the resolved shape, both refusals, the
two binds and their guard, the deployer's ordering, the planner mapping, and the
reap behaviour against a fixture (ghosts listed, then moved to the SSD trash --
files that exist only above are sidecars, not ghosts, so only directories are
candidates).

scripts/deploy-plan.py

@@ -421,6 +421,11 @@ def services_for_path(path: str, target: str) -> set[str]:
                 "tautulli": {"tautulli"},
             }
             _add(services, *quadlet_services.get(parts[1], set()))
+        if len(parts) >= 2 and parts[1] == "host":
+            # dankserver/host/systemd/mnt-media.mount is the overlay view the two
+            # media servers bind (scripts/media-view.sh installs it on the host),
+            # so editing it restarts jellyfin and plex and nothing else.
+            _add(services, "jellyfin", "plex")
         if len(parts) >= 2 and parts[1] == "observability":
             # Dankserver's node-exporter became a Quadlet unit on 2026-09-16
             # (serverAppConfigs-docs/Infrastructure/Observability.md): its
@@ -466,6 +471,10 @@ def services_for_path(path: str, target: str) -> set[str]:
             # that service (target_services then keeps it only on the host being
             # planned). Editing the collector restarts the running exporter.
             _add(services, "gpu-exporter")
+        if name == "media-view.sh":
+            # The installer is what creates, mounts and reaps the view both media
+            # servers read, so a change to it is a restart of that pair.
+            _add(services, "jellyfin", "plex")
         if name in {"frank-zealot.env", "frank-zealot.service", "serve-frank-zealot.sh"}:
             # llama.cpp frank-zealot (2026-09-16) keeps its unit, env and serve
             # files here; each one selects frank-zealot only. The ik_llama.cpp