feat(dl): add metadata, lyrics, and cover art tagging

Introduce metadata handling for online downloads:
- Embed cover art and lyrics (synced/unsynced) into MP3 files
- Save cover art to album folders and .lrc lyric files as sidecars
- Fetch and parse album/track metadata and lyrics from Deezer API
- Add user settings for artwork and lyrics embedding, LRC export, and cover quality
- Refactor queue manager to run continuously in background

src/lib/services/deezer.ts

@@ -317,6 +317,16 @@ export class DeezerAPI {
     }
   }
 
+  // Get album data
+  async getAlbumData(albumId: string): Promise<any> {
+    return this.apiCall('album.getData', { alb_id: albumId });
+  }
+
+  // Get track lyrics
+  async getLyrics(trackId: string): Promise<any> {
+    return this.apiCall('song.getLyrics', { sng_id: trackId });
+  }
+
   // Get track download URL
   async getTrackDownloadUrl(trackToken: string, format: string, licenseToken: string, retryCount: number = 0): Promise<string | null> {
     console.log('[DEBUG] Getting track download URL...', { trackToken, format, licenseToken });