[Bug]: 在自定义React组件示例中添加Snapline内置插件，对齐线优先级不是最高的，如何处理？

### Describe the bug / 问题描述

https://g6.antv.antgroup.com/examples/element/custom-node/#react-node

用的这个官方示例，配置代码如下
```js
plugins: [{
type: 'snapline',
key: 'snapline',
verticalLineStyle: { stroke: '#F08F56', lineWidth: 2, zIndex: 9999 },
horizontalLineStyle: { stroke: '#17C76F', lineWidth: 2, zIndex: 9999 },
offset: 40,
autoSnap: true,
tolerance: 8,
}]
```

### Reproduction link / 复现链接

https://g6.antv.antgroup.com/examples/element/custom-node/#react-node

### Steps to Reproduce the Bug or Issue / 重现步骤

用官方的示例即可

### Version / 版本

🆕 5.x

### OS / 操作系统

- [x] macOS
- [ ] Windows
- [ ] Linux
- [ ] Others / 其他

### Browser / 浏览器

- [x] Chrome
- [ ] Edge
- [ ] Firefox
- [ ] Safari (Limited support / 有限支持)
- [ ] IE (Nonsupport / 不支持)
- [ ] Others / 其他

Start with the React custom-node example at the linked G6 documentation URL and reproduce the configured snapline plugin behavior in Chrome. Trace how the snapline plugin's vertical and horizontal lines are rendered and ordered relative to the custom node; done means the alignment lines consistently appear above the other example elements.

Written by the indexing model from the issue text.