fix: remix detection — official audio for normal tracks, no suffix for remixes

Remix titles (remix/edit/flip/vip/etc.) are specific enough without suffix.
Normal tracks get 'official audio' to prefer audio over music videos.
Original official-audio issue was only for remixes — now caught by regex.

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

backend/novasonic-server.js

@@ -179,7 +179,10 @@ async function downloadTrack({ jobId, artist, albumArtist, title, album, year, t
   }
 
   const outputTemplate = path.join(dir, `${trackPrefix}${safeTitle}.%(ext)s`);
-  const query = `${mainArtist} - ${title}`;
+  const isRemix = /\b(remix|edit|flip|vip|bootleg|mix|rework|cover)\b/i.test(title);
+  const query   = isRemix
+    ? `${mainArtist} - ${title}`
+    : `${mainArtist} - ${title} official audio`;
 
   // Step 1: yt-dlp — audio only, no thumbnail (we embed iTunes artwork ourselves)
   const baseArgs = [