Reported via Find & Add (Billie Eilish "bad guy"): the track was in the library
and on Plex, but never showed in the modal's 20 results. Root cause (proven
against the real 307k-track DB): the search did `ORDER BY tracks.title`, which is
case-SENSITIVE in SQLite (BINARY collation sorts 'B' before 'b'). Billie's title
is lowercase "bad guy"; everyone else's is "Bad Guy", so all the capitalised ones
sorted first, filled the LIMIT, and her exact match landed at ~#25 — cut off.
- search_tracks now ranks by relevance: exact title match first (case-insensitive
via unidecode_lower), then prefix, then alphabetical — so an exact match can't
be sorted below the limit by a capital letter. Helps every caller.
- Added a rank-only `rank_artist` hint (never filters): Find & Add already knows
the source track's artist, so it now passes it and the exact title+artist match
floats to #1. Filtering was deliberately avoided — if the track is tagged under
a slightly different artist on the server, a filter would re-hide it.
Verified on the real DB: title-only "bad guy" now surfaces Billie at #4 (was
>#20); with the artist hint she's #1. Seam tests: lowercase exact title isn't
buried; rank hint floats the match without filtering; exact title beats a
superstring title. 10 tests pass.