refactor(media): mount the view inside /var/lib/media-meta instead of under /mnt

The merged door was /mnt/media, which read like a third volume and split the host
state across two trees. It is now /var/lib/media-meta/view, so the array layer,
the SSD upper layer, the kernel workdir, the reap trash and the merged tree are
one directory — and the mount table gains no new /mnt entry beside the array.

systemd names a mount unit after its ESCAPED path, so the repo copy keeps the
readable name media-meta-view.mount while `install` writes the host file as
var-lib-media\x2dmeta-view.mount; `plan` prints both and the page records them, so
nobody hunts for a unit that "does not exist". install also creates the mount
point itself, because systemd will not.

The seam now additionally pins that the unit's Where= is exactly the path both
containers bind — guard and bind cannot drift apart. The Quadlet Lifecycle
phantom-path example is corrected too: it named an invented /mnt/media/*, while
the real phantom is the legacy /opt/jellyfin/* that dankserver/compose.yaml still
carries for a service whose roots moved to /home/dank/Containers/jellyfin.

dankserver/plex/quadlet/plex.container

@@ -15,8 +15,8 @@ Volume=/var/lib/plexmediaserver:/config
 # its own database is written against it, so swapping the HOST source of this bind
 # to the overlay view re-points Plex at the sidecars without touching its DB.
 # Read-only: Plex consumes the NFO files Jellyfin writes and writes no metadata.
-Volume=/mnt/media:/mnt/entropy:ro
-UnitConfigItem=ConditionPathIsMountPoint=/mnt/media
+Volume=/var/lib/media-meta/view:/mnt/entropy:ro
+UnitConfigItem=ConditionPathIsMountPoint=/var/lib/media-meta/view
 PublishPort=32400:32400
 
 [Service]