feat: Implement mouse wheel zoom to cursor position

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

src/ViewportWidget.cpp

@@ -239,7 +239,8 @@ void ViewportWidget::mouseMoveEvent(QMouseEvent *event)
 
 void ViewportWidget::wheelEvent(QWheelEvent *event)
 {
-    m_camera->wheelEvent(event);
+    QVector3D worldPos = unproject(event->pos(), m_currentPlane);
+    m_camera->wheelEvent(event, worldPos);
 }
 
 void ViewportWidget::keyPressEvent(QKeyEvent *event)