[Feature] 瀑布图支持指定维度轴第一个作为总计

### What problem does this feature solve?

<img width="1264" height="430" alt="Image" src="https://github.com/user-attachments/assets/fbcd2f8f-fb97-46f4-b023-89f546c255df" />

### What does the proposed API look like?

NA