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/repository/song.sql.go

@@ -68,6 +68,15 @@ func (q *Queries) AddSongPlayed(ctx context.Context, arg AddSongPlayedParams) er
 	return err
 }
 
+const addSongPlayedByUUID = `-- name: AddSongPlayedByUUID :exec
+UPDATE song SET times_played = times_played + 1 WHERE uuid = $1
+`
+
+func (q *Queries) AddSongPlayedByUUID(ctx context.Context, argUuid uuid.UUID) error {
+	_, err := q.db.Exec(ctx, addSongPlayedByUUID, argUuid)
+	return err
+}
+
 const checkSong = `-- name: CheckSong :one
 SELECT COUNT(*) FROM song WHERE soundtrack_id = $1 AND path = $2
 `
@@ -181,6 +190,37 @@ func (q *Queries) FindSongsFromSoundtrack(ctx context.Context, soundtrackID int3
 	return items, nil
 }
 
+const getActiveSongByUUID = `-- name: GetActiveSongByUUID :one
+SELECT song.soundtrack_id, song.song_name, song.path, song.times_played, song.hash, song.file_name, song.uuid, song.soundtrack_uuid, 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
+`
+
+type GetActiveSongByUUIDRow struct {
+	Song           Song   `json:"song"`
+	SoundtrackName string `json:"soundtrack_name"`
+	SoundtrackPath string `json:"soundtrack_path"`
+}
+
+func (q *Queries) GetActiveSongByUUID(ctx context.Context, argUuid uuid.UUID) (GetActiveSongByUUIDRow, error) {
+	row := q.db.QueryRow(ctx, getActiveSongByUUID, argUuid)
+	var i GetActiveSongByUUIDRow
+	err := row.Scan(
+		&i.Song.SoundtrackID,
+		&i.Song.SongName,
+		&i.Song.Path,
+		&i.Song.TimesPlayed,
+		&i.Song.Hash,
+		&i.Song.FileName,
+		&i.Song.Uuid,
+		&i.Song.SoundtrackUuid,
+		&i.SoundtrackName,
+		&i.SoundtrackPath,
+	)
+	return i, err
+}
+
 const getRandomActiveSong = `-- name: GetRandomActiveSong :one
 SELECT song.soundtrack_id, song.song_name, song.path, song.times_played, song.hash, song.file_name, song.uuid, song.soundtrack_uuid, soundtrack.path AS soundtrack_path
 FROM song
@@ -285,6 +325,7 @@ const getSongsBySoundtrackUUID = `-- name: GetSongsBySoundtrackUUID :many
 SELECT soundtrack_id, song_name, path, times_played, hash, file_name, uuid, soundtrack_uuid
 FROM song
 WHERE soundtrack_uuid = $1
+ORDER BY song_name
 `
 
 func (q *Queries) GetSongsBySoundtrackUUID(ctx context.Context, soundtrackUuid uuid.UUID) ([]Song, error) {