feat: menu-bar-only app (no Dock icon) + macOS app icon

- NSApplicationActivationPolicyAccessory: app hidden from Dock and
  app switcher; lives only in the menu bar tray
- resources/clouck.icns: programmatic icon (green gradient rounded
  square, white dial, 10:10 hands), all sizes 16-1024 incl @2x
- CMake: MACOSX_BUNDLE_ICON_FILE wired, icns shipped in Resources/

clock_widget.h

@@ -42,6 +42,9 @@ public:
 
     QMenu *menu() const { return m_contextMenu; }
 
+    QString primaryTimeZoneId() const { return m_primaryTimeZoneId; }
+    QString secondaryTimeZoneId() const { return m_secondaryTimeZoneId; }
+
 protected:
     void mousePressEvent(QMouseEvent *event) override;
     void mouseMoveEvent(QMouseEvent *event) override;