Add Deezer download source: client, settings UI, ARL authentication
- New core/deezer_download_client.py: full download client with ARL auth,
Blowfish decryption, quality fallback (FLAC/MP3 320/MP3 128), search,
thread-safe download tracking. Not yet integrated into orchestrator.
- Settings UI: Deezer download quality selector, ARL token input, test
connection button. Appears in download source dropdown and hybrid list.
- Test endpoint: /api/deezer-download/test verifies ARL and returns tier.
- Added deezer_download to settings save whitelist and sensitive paths.
- Fixed Spotify enrichment worker default to unpaused (like other workers).
2ae5050ef1