feat: Implement pixel-perfect camera panning

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

src/ViewportWidget.cpp

@@ -233,7 +233,7 @@ void ViewportWidget::mouseMoveEvent(QMouseEvent *event)
         m_activeSketchTool->mouseMoveEvent(event);
     }
 
-    m_camera->mouseMoveEvent(event);
+    m_camera->mouseMoveEvent(event, height());
     update();
 }