[Bug] echarts-website should use zh-Hans / zh-hans instead of zh

### Version

14b30f1

### Link to Minimal Reproduction

https://echarts.apache.org

### Steps to Reproduce

1. Go to https://echarts.apache.org

### Current Behavior

* The "Chinese"/Mandarin version actually only provide Mandarin in Simplified Han script instead of being a place providing both Simplified Han script and Traditional Han script versions (like Wikipedia).

### Expected Behavior

* The `zh`-only language tag is for Simplified Han script + Traditional Han script writing systems. Please specify BCP 47 script subtag.
* Use either https://echarts.apache.org/zh-Hans or https://echarts.apache.org/zh-hans instead.
* Add https://echarts.apache.org/zh-Hant or https://echarts.apache.org/zh-hant for Traditional Han script if possible.

### Environment

```markdown
- OS: Kubuntu 25.04
- Browser: Firefox 142.0.1
```

### Any additional comments?

It would also be great to provide information about how to translate the online documentation website.