fix(backend): apply web_music client to YTM search extraction too

The YTM search (getYtmVideoUrls) ran without the web_music client, so yt-dlp
parsed the search page as a generic YouTube search and returned unrelated
videos instead of the native Songs shelf — the actual artist track (e.g.
qNffDItRUeo for MINA - recognize) never appeared in results. Apply the same
player_client=web_music,default arg to the search step.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/lib/ytdlp.js

@@ -220,6 +220,10 @@ async function downloadTrack({ jobId, artist, rawArtist, albumArtist, title, alb
       '--playlist-items', `1-${maxItems}`,
       '--print', 'webpage_url',
       '--no-warnings',
+      // Without the web_music client, yt-dlp parses the YTM search page as a
+      // generic YouTube search and returns unrelated videos instead of the
+      // native Songs shelf (where the actual artist track lives).
+      '--extractor-args', 'youtube:player_client=web_music,default',
     ], { env: { ...process.env, PYTHONUNBUFFERED: '1' } });
     proc.stdout.on('data', d => {
       const text = d.toString();