feat: add seamless lazy loading for genre and playlist views

Introduce paged loading with early prefetch for genre albums/playlists and playlist tracks, while preserving full-data behavior for deep shuffle and playlist play-all actions.

src/mainwindow.cpp

@@ -150,6 +150,9 @@ MainWindow::MainWindow(QobuzBackend *backend, QWidget *parent)
     connect(m_library, &List::Library::userPlaylistIdsChanged,
             this, [this](const QSet<qint64> &playlistIds) {
         m_userPlaylistIds = playlistIds;
+        const qint64 currentPlaylistId = m_content->tracksList()->playlistId();
+        if (currentPlaylistId > 0)
+            m_content->setCurrentPlaylistFollowed(m_userPlaylistIds.contains(currentPlaylistId));
     });
     connect(m_library, &List::Library::userPlaylistsChanged,
             this, &MainWindow::onUserPlaylistsChanged);
@@ -537,6 +540,13 @@ void MainWindow::onArtistLoaded(const QJsonObject &artist)
 
 void MainWindow::onPlaylistLoaded(const QJsonObject &playlist)
 {
+    const bool fullLoad = playlist["full_load"].toBool(false);
+    const int trackOffset = playlist["tracks"].toObject()["offset"].toInt(0);
+    if (!fullLoad && trackOffset > 0) {
+        m_content->tracksList()->appendPlaylistPage(playlist);
+        return;
+    }
+
     const qint64 id = static_cast<qint64>(playlist["id"].toDouble());
     const qint64 ownerId = static_cast<qint64>(playlist["owner"].toObject()["id"].toDouble());
     const qint64 myId = AppSettings::instance().userId();