Three-step redownload flow in the enhanced library view:
1. Metadata Source — searches Spotify/iTunes/Deezer simultaneously,
shows results with match scores, flags current match
2. Download Source — searches all active download sources (Soulseek,
YouTube, Tidal, etc.), shows candidates with format/bitrate/size/
confidence, flags blacklisted sources
3. Download — starts download, polls for progress, deletes old file
on success, updates DB path
Also integrates the download blacklist into the download pipeline —
_attempt_download_with_candidates now skips blacklisted sources
automatically during all downloads (wishlist, playlist sync, etc.).
New redownload button (↻) on each track row in enhanced library view.
Post-processing hook deletes old file and updates DB track path after
successful redownload.