Add write-through cache for per-item track/episode data

lidarr_cleanup.sh and sonarr_cleanup.sh already walk every artist/series
individually (trackFile/episodefile) for their own cleanup decisions --
that walk now also writes the raw per-item data through to a short-lived
tmpfs cache (arr_item_cache_write, 4h freshness, no persistent backup
since every consumer already has its own live fallback). lidarr_missing_art.sh
runs later in the same nightly window and now reads that cache first,
skipping its own redundant per-artist walk entirely on a hit. Sonarr side
is write-through only for now -- no second consumer exists yet, but the
data's there for whenever one does. Future consumers: arr_get_cached_items()
first, live per-item fetch as fallback, same pattern as these two.

Arrs_Stack/sonarr_cleanup.sh

@@ -310,9 +310,17 @@ TRACKED_FILE="$TMP_DIR/tracked_paths.txt"
 # Fetches every series' episode-file paths fresh into TRACKED_FILE/TRACKED_MAP/TRACKED_COUNT.
 # Pulled into a function so the rescan-aware retry below can re-fetch after waiting without
 # duplicating this whole loop inline.
+#
+# Write-through — also caches the raw per-episode data via arr_item_cache_write() (2026-07-17)
+# for any future script that needs Sonarr's per-episode file data — none exist yet (unlike
+# Lidarr, where lidarr_missing_art.sh already reads this), but the walk is happening regardless
+# for our own cleanup decisions, so the cache write is free by comparison. Future consumers:
+# call arr_get_cached_items("sonarr") first, fall back to your own live walk on a miss.
 _fetch_tracked_files() {
     > "$TRACKED_FILE"
     local _series_index=0
+    local all_episodes_tmp
+    all_episodes_tmp=$(mktemp)
     while IFS= read -r series_id; do
         [[ -z "$series_id" ]] && continue
         (( _series_index++ ))
@@ -320,6 +328,7 @@ _fetch_tracked_files() {
             log "Fetching files: $_series_index/$SERIES_COUNT series..."
         SERIES_FILES=$(arr_api "$SONARR_URL" "$SONARR_API_KEY" "v3" "episodefile?seriesId=${series_id}" "Sonarr" 2>/dev/null)
         if [[ -n "$SERIES_FILES" ]]; then
+            echo "$SERIES_FILES" >> "$all_episodes_tmp"
             while IFS= read -r api_path; do
                 [[ -z "$api_path" ]] && continue
                 translate_path "$api_path" >> "$TRACKED_FILE"
@@ -327,6 +336,9 @@ _fetch_tracked_files() {
         fi
     done <<< "$SERIES_IDS"
 
+    arr_item_cache_write "sonarr" "$(jq -s 'add // []' "$all_episodes_tmp" 2>/dev/null)"
+    rm -f "$all_episodes_tmp"
+
     sort -u "$TRACKED_FILE" -o "$TRACKED_FILE"
 
     # Build in-memory lookup map — O(1) per lookup vs O(n) grep per file