Library now provides GetTrackDownloadURL (signed URL via XML download_info_url), so ym-dl delegates to it instead of reimplementing XML parsing and MD5 signing. Removed local DownloadTrackXML/DownloadInfoXML and unused crypto/md5, encoding/hex, encoding/xml, io imports from client.go. Track.Lyrics replaced by LyricsInfo (availability flags only, no text). Lyrics text requires separate GetTrackLyrics + GetTrackLyricsText calls — not implemented yet, lyrics field left empty.