Add full-featured SpotifyWorker and iTunesWorker background workers to enrich artists, albums, and tracks with external metadata using batch cascading searches, fuzzy name matching, ID validation, and DB backfills. Update RepairWorker to re-read the transfer path from the database each scan, resolve host paths when running in Docker, and trigger immediate rescans when the transfer path changes; remove the static config_manager dependency. Also include supporting changes to the database layer and web UI/server (stats, controls, and styles) to integrate the new workers and reflect updated worker status.
