fix: detect followed playlists correctly in header

Load owner+subscriber playlists, track all playlist IDs for follow-state resolution, and keep audio ring buffer at 32k as requested.

src/mainwindow.hpp

@@ -55,6 +55,7 @@ private:
     QobuzBackend    *m_backend     = nullptr;
     PlayQueue       *m_queue       = nullptr;
     QVector<QPair<qint64, QString>> m_userPlaylists;
+    QSet<qint64> m_userPlaylistIds;
     QSet<QString> m_favAlbumIds;
     QSet<qint64> m_favArtistIds;
     bool m_showFavAlbumsOnLoad = false;