Uploads library on the USB drive with a nightly stable-disk copy; Topic channels resolve by name

- UPLOAD_DIR moves to the USB drive; reads fall back to UPLOAD_BACKUP_DIR on the
  ytplayer-data volume, and while the drive is offline new uploads land there
- scripts/ops/uploads-backup.sh (homelab cron, 03:30) copies both ways, never
  deletes; the server removes a deleted upload from both places
- /api/channel resolves a bare channel name ('Artist - Topic') to its id via a
  search, and the client falls back to the channel name for old saved entries

scripts/ops/uploads-backup.sh

@@ -0,0 +1,29 @@
+#!/bin/sh
+# Nightly second copy of the ytplayer uploads library (homelab host, cron).
+#
+#   USB drive (primary):   /mnt/data/ytplayer/uploads
+#   stable disk (backup):  <ytplayer-data volume>/uploads-backup
+#
+# Copies new files both ways and never deletes: the server removes a deleted
+# upload from both places itself, and anything uploaded while the drive was
+# offline (written to the backup) is copied back onto the drive here.
+set -eu
+VOL=${VOL:-/var/lib/docker/volumes/ytplayer-main-1dihzn_ytplayer-data/_data}
+USB=/mnt/data/ytplayer
+MIN_FREE_KB=${MIN_FREE_KB:-20971520}   # keep 20 GiB free on the stable disk
+log() { logger -t ytplayer-uploads-backup "$*"; echo "$*"; }
+
+[ -f "$USB/.hl-data" ] || { log "USB drive offline (no marker) — skipped"; exit 0; }
+mkdir -p "$USB/uploads" "$VOL/uploads-backup"
+
+need=$(du -sk "$USB/uploads" | cut -f1)
+have=$(du -sk "$VOL/uploads-backup" | cut -f1)
+free=$(df -Pk "$VOL" | awk 'NR==2{print $4}')
+if [ $((free - (need - have))) -lt "$MIN_FREE_KB" ]; then
+  log "not enough room on the stable disk for the backup (free ${free} KB, need ~$((need - have)) KB more) — skipped"
+  exit 1
+fi
+
+rsync -a --update "$USB/uploads/" "$VOL/uploads-backup/"   # newer wins (e.g. replaced cover art)
+rsync -a --update "$VOL/uploads-backup/" "$USB/uploads/"
+log "ok — $(ls "$USB/uploads" | wc -l) files, $(du -sh "$USB/uploads" | cut -f1)"