Wait up to 6 hours for Nextcloud's borg lock before deferring the weekly media backup

AIO's borg now runs daily from 07:30 UTC for about 2 hours, so the Saturday
05:00 fire can find the lock held and skip the whole week, which trips Uptime
Kuma's 8-day push window. Poll the lock every 5 minutes for up to 6 hours and
defer only if it is still held after that.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

server/home/systemd/media-backup.timer

@@ -6,8 +6,9 @@ Description=Weekly Media -> Backup pool copy
 # timeshift (04:00), arr-queue-reconcile (04:31), and both ~/Server backups (01:00, 02:00).
 # Saturday specifically because Monday carries the Media scrub and Sunday has
 # raid-check (01:00), docker-prune (05:33) and dind-prune (06:03).
-# gib also runs Nextcloud's borg by hand roughly monthly and is, in his words,
-# not going to be doing that at 5 AM on a Saturday -- so the borg lock should be free.
+# Nextcloud AIO's borg runs daily from 07:30 UTC for about 2 hours, so its lock can
+# overlap this fire. The script waits up to 6 h for the lock, checking every 5 min,
+# and defers the week only if borg is still running after that.
 OnCalendar=Sat *-*-* 05:00:00
 RandomizedDelaySec=15m
 Persistent=true