fix: iTunes artist match and MusicBrainz first-artist-only query

iTunes: split artist by [\s,;/] not just space so "VXLLAIN, iGRES"
yields first word "vxllain" (no trailing comma) and matches correctly.

MusicBrainz: extract first artist from the full credit string (split on
,;&•) and use `artistname` field — MB stores credits like "VXLLAIN feat.
iGRES & ENXK" which never matched the comma-joined full string.

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

backend/novasonic-server.js

@@ -553,7 +553,9 @@ app.get('/api/musicbrainz/lookup', async (req, res) => {
   const { artist, title } = req.query;
   if (!artist || !title) return res.status(400).json({ error: 'artist and title required' });
   try {
-    const query = `recording:"${title.replace(/"/g, '')}" AND artist:"${artist.replace(/"/g, '')}"`;
+    // Use only the first artist — MB won't match "VXLLAIN, iGRES, ENXK" against "VXLLAIN feat. iGRES & ENXK"
+    const firstArtist = artist.split(/[,;&•]/)[0].trim().replace(/"/g, '');
+    const query = `recording:"${title.replace(/"/g, '')}" AND artistname:"${firstArtist}"`;
     const url = `https://musicbrainz.org/ws/2/recording/?query=${encodeURIComponent(query)}&fmt=json&limit=5`;
     const r = await fetch(url, { headers: { 'User-Agent': 'NovaSonic/1.0 (me_honeyy@proton.me)' }, signal: AbortSignal.timeout(10000) });
     if (!r.ok) return res.status(502).json({ error: `MusicBrainz ${r.status}` });