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_radarr_discovery.sh

@@ -485,7 +485,10 @@ fi
 echo ""
 echo "━━━ $ICON_SYNC Existing Libraries ━━━"
 
-RADARR_MOVIES_JSON=$(_radarr_get "movie") || { error "Could not fetch Radarr library"; exit 1; }
+# Cache-first — arr_get_tracked_data() serves the shared cache when it's fresh (kept current
+# every 30min by arr_cache_prefill.sh in CRITICAL_MAINTENANCE_SCRIPTS), falls back to a live
+# fetch when it's stale, and waits out an active rescan before either.
+RADARR_MOVIES_JSON=$(arr_get_tracked_data "radarr" "$RADARR_URL" "$RADARR_API_KEY" "v3") || { error "Could not fetch Radarr library"; exit 1; }
 
 declare -A RADARR_TMDB   # tmdb_id → 1
 while read -r tmdb_id; do