导入的MJCF文件模型会上移

<img width="241" height="108" alt="Image" src="https://github.com/user-attachments/assets/4aac69dc-bf9d-41c7-a6c6-53c7e20d44c9" />

MJCF是：
```xml
<mujoco model="parallel_gripper">
  <worldbody>
    <geom size="0.1" />
  </worldbody>
</mujoco>
```