Put everything Varaverk persists under one root, state included

common.sh

@@ -2505,7 +2505,7 @@ arr_cache_file() { echo "${ARR_CACHE_DIR}/${1}_tracked_cache.json"; }
 # every write, so it's never more than one write-cycle stale (2026-07-17). Exists purely so a
 # reboot doesn't leave the tmpfs cache genuinely empty until the next live fetch completes —
 # not a source of truth in its own right, just what tmpfs gets restored from when missing.
-arr_cache_backup_file() { echo "${DATA_DIR}/${1}_tracked_cache.json"; }
+arr_cache_backup_file() { echo "${ARR_CACHE_BACKUP_DIR}/${1}_tracked_cache.json"; }
 
 arr_rescan_duration_db() { echo "${DATA_DIR}/${1}_rescan_duration.db"; }