fix: Emulate middle click with left + right mouse button for camera controls

Co-authored-by: aider (gemini/gemini-2.5-pro) <aider@aider.chat>

src/Camera.cpp

@@ -27,7 +27,7 @@ void Camera::mouseMoveEvent(QMouseEvent* event, int viewportHeight)
     int dx = event->pos().x() - m_lastPos.x();
     int dy = event->pos().y() - m_lastPos.y();
 
-    if (event->buttons() & Qt::MiddleButton) {
+    if ((event->buttons() & Qt::MiddleButton) || (event->buttons() == (Qt::LeftButton | Qt::RightButton))) {
         if (QApplication::keyboardModifiers() & Qt::ShiftModifier) {
             // Pan
             if (viewportHeight == 0) viewportHeight = 1;