fix(web): metadata autofill normalizes trailing " & " in multi-artist lists

Apple Music / MusicBrainz render multi-artist credits as "A, B, C & D" — the last
artist is joined with " & " instead of the list separator, so it stayed glued to the
previous one (e.g. "REI AMI & KPop Demon Hunters Cast" became a single artist that
Navidrome's ";" split could not break apart).

_fmtArtists now also rewrites " & " to the list separator, but only when the string
is already a list (contains ; , • ·), so real band names like "Simon & Garfunkel"
stay intact. The iTunes and MusicBrainz autofill results are now run through
_fmtArtists too (previously set raw), so the artist field comes out ";"-separated
and matches the Navidrome Tags.artist.Split config.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ui/metadata.js

@@ -8,7 +8,14 @@ import { showConfirm } from './modals.js';
 // ─── SONG INFO MODAL ───
 function _fmtArtists(str, sep) {
   if (!str) return '';
-  return str.split(/\s*[•·;,]\s*/).map(s => s.trim()).filter(Boolean).join(sep);
+  let s = str.trim();
+  // Apple Music / MusicBrainz render multi-artist lists as "A, B, C & D" — the LAST artist is
+  // joined with " & " instead of the list separator, which would otherwise stay glued together as
+  // one artist. Only rewrite the " & " when the string is already a list (contains ; , • ·), so
+  // genuine band names like "Simon & Garfunkel" or "Earth, Wind & Fire" without a leading list are
+  // left intact. (Manual editor — the user can still fix the rare false positive before saving.)
+  if (/[;,•·]/.test(s)) s = s.replace(/\s+&\s+/g, '; ');
+  return s.split(/\s*[•·;,]\s*/).map(x => x.trim()).filter(Boolean).join(sep);
 }
 
 function _renderInfoModal(s) {
@@ -178,8 +185,8 @@ export async function autofillMusicBrainz() {
     const d = await r.json();
     if (!d.found) { status.textContent = '❌ Kein Treffer auf MusicBrainz'; return; }
     if (d.title)       document.getElementById('ie-title').value       = d.title;
-    if (d.artist)      document.getElementById('ie-artist').value      = d.artist;
-    if (d.albumArtist) document.getElementById('ie-albumartist').value = d.albumArtist;
+    if (d.artist)      document.getElementById('ie-artist').value      = _fmtArtists(d.artist, '; ');
+    if (d.albumArtist) document.getElementById('ie-albumartist').value = _fmtArtists(d.albumArtist, ', ');
     if (d.album)       document.getElementById('ie-album').value       = d.album;
     if (d.genre)       document.getElementById('ie-genre').value       = d.genre;
     if (d.year)        document.getElementById('ie-year').value        = d.year;
@@ -213,8 +220,8 @@ export async function autofillItunes() {
     const d = await r.json();
     if (!d.found) { status.textContent = '❌ Kein Treffer auf iTunes'; return; }
     if (d.title)       document.getElementById('ie-title').value       = d.title;
-    if (d.artist)      document.getElementById('ie-artist').value      = d.artist;
-    if (d.albumArtist) document.getElementById('ie-albumartist').value = d.albumArtist;
+    if (d.artist)      document.getElementById('ie-artist').value      = _fmtArtists(d.artist, '; ');
+    if (d.albumArtist) document.getElementById('ie-albumartist').value = _fmtArtists(d.albumArtist, ', ');
     if (d.album)       document.getElementById('ie-album').value       = d.album;
     if (d.genre)       document.getElementById('ie-genre').value       = d.genre;
     if (d.year)        document.getElementById('ie-year').value        = d.year;