Move the web watchlist scan core onto the shared metadata source priority so primary provider settings are respected during artist, album, and image resolution.
Add coverage for primary-source-first discography lookup and fallback to later providers when the primary source has no albums.
Bring placeholder tracklist skipping back into the shared watchlist scan path, and centralize the DB-only artist image backfill helper so both web scan entrypoints reuse the same logic.
Move the shared watchlist scan loop into core/watchlist_scanner.py so web_server.py only handles triggers, locks, progress, and post-scan orchestration.
Manual and scheduled watchlist scans now share the same scanner-side core, while the web entrypoints keep profile selection and automation progress updates.
