fix: use US iTunes genre to avoid Japanese-localized genre names

JP store returns localized genres (e.g. イージーリスニング instead of Easy Listening).
Fetch JP and US in parallel, use JP match for title/album/artwork but always
take genre from US result so genre is always in English/Western characters.

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

backend/lib/metadata.js

@@ -112,15 +112,14 @@ async function lookupItunesTrackMeta(artist, title) {
     );
     const titleOnlyMatch = results => results.find(t => normalizeTitle(t.trackName) === normT);
 
-    // Strategy: JP strict → US strict → US title-only (never JP title-only to avoid
-    // false positives where JP returns a different Japanese song with the same English title)
-    const jpResults = await fetchItunes('jp');
+    // Fetch both in parallel — JP for correct Japanese titles/artwork, US for English genre names
+    const [jpResults, usResults] = await Promise.all([fetchItunes('jp'), fetchItunes('us')]);
     let match = strictMatch(jpResults);
-    if (!match) {
-      const usResults = await fetchItunes('us');
-      match = strictMatch(usResults) || titleOnlyMatch(usResults);
-    }
+    let usMatch = strictMatch(usResults) || titleOnlyMatch(usResults);
+    if (!match) match = usMatch;
     if (!match) return {};
+    // JP genre names are localized (e.g. イージーリスニング); always prefer US genre
+    const genre = (usMatch || match).primaryGenreName;
     return {
       album:            match.collectionName || '',
       year:             match.releaseDate ? new Date(match.releaseDate).getFullYear() : undefined,
@@ -128,7 +127,7 @@ async function lookupItunesTrackMeta(artist, title) {
       totalTracks:      match.trackCount    || undefined,
       discNum:          match.discNumber    || undefined,
       discTotal:        match.discCount     || undefined,
-      genre:            match.primaryGenreName || undefined,
+      genre:            genre               || undefined,
       artworkUrl:       (match.artworkUrl100 || '').replace('100x100bb', '1000x1000bb'),
       durationMs:       match.trackTimeMillis  || undefined,
       itunesArtistName: match.artistName       || undefined,