Implement songLyrics extension: getLyricsBySongId with real word/syllable cues

Adds getLyricsBySongId (versions 1 and 2 of the songLyrics extension,
gated by the enhanced param): returns every stored structuredLyrics
entry for a song, including line-level start times for synced lyrics
and, only when a source actually provided word/syllable timing (an
Enhanced LRC sidecar) and enhanced=true was requested, cueLine/cue
data with the precomputed UTF-8 byte offsets. Plain and non-enhanced
synced lyrics never get fabricated cue data.

Removes the now-dead SetSongLyrics writer (superseded by
database.InsertLyrics); SongLyricsPlainText keeps serving the legacy
getLyrics endpoint unchanged.

Adds a scanner integration test proving a sidecar .lrc (with an
Enhanced LRC line) is discovered and indexed during a real scan.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014r98AtcBbevpscWLsfwVvv

internal/database/subsonic_helpers2.go

@@ -143,58 +143,6 @@ func AlbumsByRecentlyPlayed(db *sql.DB, userID string, limit, offset int) ([]*Al
 	return scanAlbums(rows)
 }
 
-// SetSongLyrics replaces a song's stored (unsynced) lyrics with
-// plainText, split into lines. Called by the scanner when a file has
-// embedded lyrics.
-func SetSongLyrics(db *sql.DB, songID, language, plainText string) error {
-	tx, err := db.Begin()
-	if err != nil {
-		return err
-	}
-	defer tx.Rollback()
-
-	if _, err := tx.Exec(`DELETE FROM lyrics WHERE song_id = ?`, songID); err != nil {
-		return err
-	}
-	if plainText == "" {
-		return tx.Commit()
-	}
-	lyricsID := idgen.New("ly")
-	if _, err := tx.Exec(`INSERT INTO lyrics (id, song_id, language, source, synced) VALUES (?, ?, ?, 'embedded', 0)`,
-		lyricsID, songID, language); err != nil {
-		return err
-	}
-	for i, line := range splitLines(plainText) {
-		if _, err := tx.Exec(`INSERT INTO lyrics_lines (id, lyrics_id, line_index, text) VALUES (?, ?, ?, ?)`,
-			idgen.New("ll"), lyricsID, i, line); err != nil {
-			return err
-		}
-	}
-	return tx.Commit()
-}
-
-func splitLines(s string) []string {
-	var lines []string
-	start := 0
-	for i := 0; i < len(s); i++ {
-		if s[i] == '\n' {
-			line := s[start:i]
-			line = trimCR(line)
-			lines = append(lines, line)
-			start = i + 1
-		}
-	}
-	lines = append(lines, trimCR(s[start:]))
-	return lines
-}
-
-func trimCR(s string) string {
-	if len(s) > 0 && s[len(s)-1] == '\r' {
-		return s[:len(s)-1]
-	}
-	return s
-}
-
 // SongLyricsPlainText returns a song's stored lyrics as plain text
 // (lines joined with "\n"), and whether any were found.
 func SongLyricsPlainText(db *sql.DB, songID string) (string, bool, error) {