feat: most-popular search as default Top Results tab

Add /most-popular/get endpoint support (discovered via Burp):
- Returns mixed artists/albums/tracks ordered by popularity for a query
- New 'Top Results' tab shown first/default in the search panel
- Badge column: A (artist, blue), H (hi-res album, gold), A (album, gray), T (track, green)
- Full context menu support on all item types in the new tab
- Both most-popular and regular search fire on submit in parallel

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

src/backend/qobuzbackend.cpp

@@ -51,6 +51,11 @@ void QobuzBackend::search(const QString &query, quint32 offset, quint32 limit)
     qobuz_backend_search(m_backend, query.toUtf8().constData(), offset, limit);
 }
 
+void QobuzBackend::mostPopularSearch(const QString &query, quint32 limit)
+{
+    qobuz_backend_most_popular_search(m_backend, query.toUtf8().constData(), limit);
+}
+
 void QobuzBackend::getAlbum(const QString &albumId)
 {
     qobuz_backend_get_album(m_backend, albumId.toUtf8().constData());
@@ -241,6 +246,9 @@ void QobuzBackend::onEvent(int eventType, const QString &json)
     case EV_SEARCH_OK:
         emit searchResult(obj);
         break;
+    case 26: // EV_MOST_POPULAR_OK
+        emit mostPopularResult(obj);
+        break;
     case EV_SEARCH_ERR:
         emit error(obj["error"].toString());
         break;