Spotify API and SQLite improvements

This PR improves the Spotify API integration and significantly enhances the SQLite database handling to fix concurrency issues. **Spotify API updates:** - Switched to the Spotify Developer API using client credentials authentication. - Added support for reading credentials from a JSON file and caching access tokens with expiration handling. - Fixed regex patterns for Spotify URLs to handle international URLs correctly. **Database improvements:** - Prevented "database is locked" errors by adding explicit rows.Close() calls inside loops instead of deferring them, reducing the number of open cursors. - Added SQLite busy timeout to the connection string to handle concurrent access better. - Ensured transactions are correctly committed or rolled back on errors for stability.