feat: spotify-style toolbar layout

Three-column layout matching spotify-qt:
- Left: album art thumbnail + track title/artist (stacked, 2 lines)
- Center: prev/play/next controls above elapsed / progress / total
- Right: volume button, shuffle, queue toggle, search toggle

Controls and toggles use QToolButton directly instead of QAction so the
layout is driven by HBoxLayout + VBoxLayout with equal stretch on left
and right, keeping the player controls perfectly centred at all widths.

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

src/view/maintoolbar.hpp

@@ -9,7 +9,6 @@
 #include <QToolBar>
 #include <QToolButton>
 #include <QLabel>
-#include <QAction>
 #include <QNetworkAccessManager>
 #include <QNetworkReply>
 #include <QJsonObject>
@@ -50,18 +49,23 @@ private:
     QobuzBackend *m_backend = nullptr;
     PlayQueue    *m_queue   = nullptr;
 
-    QLabel          *m_artLabel   = nullptr;
-    QLabel          *m_trackLabel = nullptr;
-    ClickableSlider *m_progress   = nullptr;
-    QLabel          *m_timeLabel  = nullptr;
-    VolumeButton    *m_volume     = nullptr;
+    // Left
+    QLabel       *m_artLabel     = nullptr;
+    QLabel       *m_trackLabel   = nullptr;
 
-    QAction *m_previous  = nullptr;
-    QAction *m_playPause = nullptr;
-    QAction *m_next      = nullptr;
-    QAction *m_shuffle   = nullptr;
-    QAction *m_queueBtn  = nullptr;
-    QAction *m_search    = nullptr;
+    // Center
+    QToolButton  *m_prevBtn      = nullptr;
+    QToolButton  *m_playBtn      = nullptr;
+    QToolButton  *m_nextBtn      = nullptr;
+    ClickableSlider *m_progress  = nullptr;
+    QLabel       *m_elapsedLabel = nullptr;
+    QLabel       *m_totalLabel   = nullptr;
+
+    // Right
+    VolumeButton *m_volume       = nullptr;
+    QToolButton  *m_shuffleBtn   = nullptr;
+    QToolButton  *m_queueBtn     = nullptr;
+    QToolButton  *m_searchBtn    = nullptr;
 
     QNetworkAccessManager *m_nam = nullptr;
     QString  m_currentArtUrl;