Make all arr library-list fetches cache-first with live fallback

Every script that fetches the full Lidarr/Sonarr/Radarr tracked-library
list now goes through arr_get_tracked_data() instead of hitting the API
directly -- cache-first when fresh, live fetch as fallback when stale,
waits out an active rescan before either. Per-item file data (trackFile/
episodefile/moviefile) stays live-only everywhere, since that's the
actual disk-truth these scripts' decisions depend on and was never part
of what's cached.

Also adds arr_cache_prefill.sh to CRITICAL_MAINTENANCE_SCRIPTS (30min
tier) with a short 1min wait ceiling, so the cache stays consistently
fresh instead of only refreshing whenever some other script happens to
write through. A full cache refresh for all three arrs measured at ~12s
total live -- nothing like the multi-hour cost of an actual rescan.

Arrs_Stack/playback_aware_lidarr_discovery.sh

@@ -516,7 +516,10 @@ fi
 echo ""
 echo "━━━ $ICON_SYNC Existing Libraries ━━━"
 
-LIDARR_ARTISTS_JSON=$(_lidarr_get "artist") || { error "Could not fetch Lidarr artists"; exit 1; }
+# Cache-first — arr_get_tracked_data() serves the shared cache when it's fresh (kept current
+# every 30min by arr_cache_prefill.sh in CRITICAL_MAINTENANCE_SCRIPTS), falls back to a live
+# fetch when it's stale, and waits out an active rescan before either.
+LIDARR_ARTISTS_JSON=$(arr_get_tracked_data "lidarr" "$LIDARR_URL" "$LIDARR_API_KEY" "v1") || { error "Could not fetch Lidarr artists"; exit 1; }
 LIDARR_NAMES=$(echo "$LIDARR_ARTISTS_JSON" | jq -r '.[].artistName' 2>/dev/null)
 LIDARR_COUNT=$(echo "$LIDARR_NAMES" | grep -c . 2>/dev/null || echo 0)
 log "$LIDARR_COUNT artists in Lidarr"