feat: convert feat./ft./featuring to / in artist tag for Navidrome split

Navidrome splits artist tags on "/" so "Drake / Rihanna" becomes two
separate artist entries. navidromeArtist() converts iTunes featuring
patterns before writing the ID3 artist tag. album_artist stays clean
(main artist only) for correct album grouping.

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

backend/novasonic-server.js

@@ -56,6 +56,16 @@ function sanitize(s) {
   return (s || 'Unknown').replace(/[\\/:*?"<>|]/g, '_').trim().slice(0, 100);
 }
 
+// Convert "Artist feat. B" / "Artist ft. B" / "Artist featuring B" → "Artist / B"
+// so Navidrome splits on "/" and lists each as a separate artist
+function navidromeArtist(name) {
+  if (!name) return name;
+  return name
+    .replace(/\s+feat\.?\s+/gi, ' / ')
+    .replace(/\s+ft\.?\s+/gi, ' / ')
+    .replace(/\s+featuring\s+/gi, ' / ');
+}
+
 function updateJob(id, update) {
   const job = jobs.get(id);
   if (job) jobs.set(id, { ...job, ...update, updatedAt: Date.now() });
@@ -179,7 +189,7 @@ async function downloadTrack({ jobId, artist, albumArtist, title, album, year, t
       '-map_metadata',  '-1',         // strip all existing tags (removes blurry YT thumbnail)
       '-id3v2_version', '3',
       '-metadata', `title=${title}`,
-      '-metadata', `artist=${artist}`,
+      '-metadata', `artist=${navidromeArtist(artist)}`,
       '-metadata', `album_artist=${mainArtist}`,
     );
     if (album)       ffArgs.push('-metadata', `album=${album}`);