getRandomSongs used a single ORDER BY random() over the media_file table. At large
library sizes that forces SQLite to scan the wide table and sort every matching row
before applying the limit — roughly 4 seconds for a 1M-track library, regardless of how
many songs are requested.
Add MediaFileRepository.GetRandom, which does this in two passes: first select N random
rowids over a narrow index (filters + library scope only, no wide columns or joins), so
the random sort runs over compact, index-friendly data; then hydrate just those rows with
the full select. The wide media_file row is never part of the sort. End-to-end this drops
getRandomSongs from ~4s to ~0.3s on a 1M-track library, and the cost no longer grows with
the requested size.
The handler now calls GetRandom directly. The filter helper that builds the genre/year
filters is renamed SongsByRandom -> SongsByGenreAndYearRange to reflect what it does, since
the random ordering is now owned by GetRandom rather than a Sort option. Filters (genre,
year, library) compose into the first pass unchanged. The album random list path is left
as-is (far fewer rows, already fast).
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