Add per-server toggle for AudioMuse-style discovery: Instant Mix via
getSimilarSongs, server similar artists instead of Last.fm on artist pages,
and higher similar-artist count in Now Playing when enabled.
When browsing a single music folder, filter similar/top song results by
album ids from that scope (Navidrome does not apply musicFolderId to those
endpoints). Request larger similar batches under a narrow scope.
Keep radio-from-track as two blocks (shuffled top songs, then shuffled
similar-by-artist) so it differs from Instant Mix. Show Alpha badge beside
the setting. Add research/ to .gitignore.