feat: pagination, back/forward nav, context menu, artist fav, image fix

**Artist portrait**
- Fix CDN URL: images.portrait.{hash,format} →
  https://static.qobuz.com/images/artists/covers/large/{hash}.{format}

**Section alignment**
- Qt::ToolButtonTextOnly on all section toggles so text is truly left-aligned

**Auth 401 race condition**
- qobuz_backend_set_token now uses blocking_lock() instead of spawning an
  async task, guaranteeing the token is set before any subsequent API call

**Pagination (infinite scroll)**
- Release sections load 50 at a time (was 500)
- ArtistSection tracks has_more + loaded count; scrolling to the bottom
  emits loadMoreRequested → ArtistView calls getArtistReleases(offset=N)
- AlbumListView gains addAlbums() for append; setReleases routes to
  setAlbums (offset=0) or appendAlbums (offset>0)

**Back/Forward navigation**
- MainToolBar exposes Back/Forward QActions (go-previous/go-next icons)
- MainWindow keeps a NavPage vector + index; pushNav() on every album/artist
  navigation; goBack/goForward re-navigate without pushing history

**Context menu on now-playing label**
- Right-click on track label in toolbar → "Go to Album" / "Go to Artist"
- MainToolBar stores current track; emits albumRequested/artistRequested
  signals wired to MainWindow's existing handlers

**Artist favourites button**
- ♡ Favourite / ♥ Favourited toggle in artist header
- Calls new addFavArtist / removeFavArtist (Rust + Qt backend wiring)

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

src/view/maintoolbar.hpp

@@ -24,9 +24,14 @@ public:
     void setCurrentTrack(const QJsonObject &track);
     void updateProgress(quint64 position, quint64 duration);
 
+    QAction *backAction()    const { return m_back; }
+    QAction *forwardAction() const { return m_fwd;  }
+
 signals:
     void searchToggled(bool visible);
     void queueToggled(bool visible);
+    void albumRequested(const QString &albumId);
+    void artistRequested(qint64 artistId);
 
 protected:
     void resizeEvent(QResizeEvent *event) override;
@@ -52,6 +57,8 @@ private:
     QobuzBackend *m_backend = nullptr;
     PlayQueue    *m_queue   = nullptr;
 
+    QAction         *m_back        = nullptr;
+    QAction         *m_fwd         = nullptr;
     QLabel          *m_artLabel    = nullptr;
     QLabel          *m_trackLabel  = nullptr;
     QAction         *m_previous    = nullptr;
@@ -67,7 +74,8 @@ private:
     QAction         *m_search      = nullptr;
 
     QNetworkAccessManager *m_nam = nullptr;
-    QString  m_currentArtUrl;
-    bool     m_playing  = false;
-    bool     m_seeking  = false;
+    QString     m_currentArtUrl;
+    QJsonObject m_currentTrack;
+    bool        m_playing = false;
+    bool        m_seeking = false;
 };