Prefer UUIDs in the API (Phase 3 of the UUID migration)

- New /api/v1 endpoints: GET /soundtracks, /soundtracks/{uuid},
  /songs/{uuid} and /songs/{uuid}/file (streams the song, Range support,
  locked during sync)
- UUIDs added to every response with soundtracks or songs: queue info and
  list (SoundtrackUuid, SongUuid) and statistics (soundtrack_uuid,
  song_uuid). Existing fields stay for backward compatibility
- Play counts and broken-song removal use song UUIDs instead of
  soundtrack ID + song name, so songs with the same name are counted
  separately
- Statistics return an empty song list for soundtracks without songs
  instead of a single empty entry
- The legacy .id file cleanup stays until Phase 4 (#31)

Closes #29

internal/db/queries/song.sql

@@ -46,7 +46,8 @@ DELETE FROM song WHERE uuid = ANY(sqlc.arg(uuids)::uuid[]);
 -- name: GetSongsBySoundtrackUUID :many
 SELECT *
 FROM song
-WHERE soundtrack_uuid = $1;
+WHERE soundtrack_uuid = $1
+ORDER BY song_name;
 
 -- name: GetSongUUIDsBySoundtrackId :many
 SELECT uuid, soundtrack_uuid FROM song WHERE soundtrack_id = $1;
@@ -62,3 +63,12 @@ JOIN soundtrack ON soundtrack.id = song.soundtrack_id
 WHERE soundtrack.deleted IS NULL
 ORDER BY random()
 LIMIT 1;
+
+-- name: AddSongPlayedByUUID :exec
+UPDATE song SET times_played = times_played + 1 WHERE uuid = $1;
+
+-- name: GetActiveSongByUUID :one
+SELECT sqlc.embed(song), soundtrack.soundtrack_name, soundtrack.path AS soundtrack_path
+FROM song
+JOIN soundtrack ON soundtrack.id = song.soundtrack_id
+WHERE song.uuid = $1 AND soundtrack.deleted IS NULL;