fix: remove space and / as artist separators, keep &

Separators: • · ; , & — space and / removed to avoid breaking multi-word artist names.

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

backend/lib/metadata.js

@@ -13,7 +13,7 @@ function navidromeArtist(name) {
     .replace(/\s+ft\.?\s+/gi, ';')
     .replace(/\s+featuring\s+/gi, ';')
     .replace(/\s+&\s+/g, ';')
-    .replace(/\s*\/\s*/g, ';')
+
     .replace(/,\s*/g, ';');
 }