fix: use 'audio' instead of 'official audio' in search query

'official audio' biased towards artist's main channel (wrong for remixes).
No suffix caused piano covers to rank top. 'audio' filters covers/tutorials
without over-specifying to official channels.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/novasonic-server.js

@@ -179,7 +179,7 @@ async function downloadTrack({ jobId, artist, albumArtist, title, album, year, t
   }
 
   const outputTemplate = path.join(dir, `${trackPrefix}${safeTitle}.%(ext)s`);
-  const query          = `${mainArtist} - ${title}`;
+  const query          = `${mainArtist} - ${title} audio`;
 
   // Step 1: yt-dlp — audio only, no thumbnail (we embed iTunes artwork ourselves)
   const baseArgs = [