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/mainwindow.cpp

@@ -169,6 +169,25 @@ MainWindow::MainWindow(QobuzBackend *backend, QWidget *parent)
     connect(m_toolBar, &MainToolBar::queueToggled,
             this, [this](bool v) { m_queuePanel->setVisible(v); });
 
+    connect(m_toolBar->backAction(),    &QAction::triggered, this, [this] {
+        if (m_navIndex <= 0) return;
+        --m_navIndex;
+        m_navFromHistory = true;
+        navigateTo(m_navHistory[m_navIndex]);
+        m_navFromHistory = false;
+        updateNavButtons();
+    });
+    connect(m_toolBar->forwardAction(), &QAction::triggered, this, [this] {
+        if (m_navIndex >= m_navHistory.size() - 1) return;
+        ++m_navIndex;
+        m_navFromHistory = true;
+        navigateTo(m_navHistory[m_navIndex]);
+        m_navFromHistory = false;
+        updateNavButtons();
+    });
+    connect(m_toolBar, &MainToolBar::albumRequested,  this, &MainWindow::onSearchAlbumSelected);
+    connect(m_toolBar, &MainToolBar::artistRequested, this, &MainWindow::onSearchArtistSelected);
+
     // Apply playback options from saved settings
     m_backend->setReplayGain(AppSettings::instance().replayGainEnabled());
     m_backend->setGapless(AppSettings::instance().gaplessEnabled());
@@ -359,12 +378,16 @@ void MainWindow::onPlayTrackRequested(qint64 trackId)
 
 void MainWindow::onSearchAlbumSelected(const QString &albumId)
 {
+    NavPage p; p.type = NavPage::Album; p.albumId = albumId;
+    pushNav(p.type, p.albumId);
     m_backend->getAlbum(albumId);
     statusBar()->showMessage(tr("Loading album…"));
 }
 
 void MainWindow::onSearchArtistSelected(qint64 artistId)
 {
+    NavPage p; p.type = NavPage::Artist; p.artistId = artistId;
+    pushNav(p.type, {}, p.artistId);
     m_backend->getArtist(artistId);
     statusBar()->showMessage(tr("Loading artist…"));
 }
@@ -389,3 +412,39 @@ void MainWindow::onUserPlaylistsChanged(const QVector<QPair<qint64, QString>> &p
     m_userPlaylists = playlists;
     m_content->tracksList()->setUserPlaylists(playlists);
 }
+
+void MainWindow::pushNav(NavPage::Type type, const QString &albumId, qint64 artistId)
+{
+    if (m_navFromHistory) return;
+    // Truncate any forward history
+    while (m_navHistory.size() > m_navIndex + 1)
+        m_navHistory.removeLast();
+    NavPage p;
+    p.type     = type;
+    p.albumId  = albumId;
+    p.artistId = artistId;
+    m_navHistory.push_back(p);
+    m_navIndex = m_navHistory.size() - 1;
+    updateNavButtons();
+}
+
+void MainWindow::navigateTo(const NavPage &page)
+{
+    switch (page.type) {
+    case NavPage::Album:
+        m_backend->getAlbum(page.albumId);
+        statusBar()->showMessage(tr("Loading album…"));
+        break;
+    case NavPage::Artist:
+        m_backend->getArtist(page.artistId);
+        statusBar()->showMessage(tr("Loading artist…"));
+        break;
+    default: break;
+    }
+}
+
+void MainWindow::updateNavButtons()
+{
+    m_toolBar->backAction()->setEnabled(m_navIndex > 0);
+    m_toolBar->forwardAction()->setEnabled(m_navIndex < m_navHistory.size() - 1);
+}