request for a demo that showing a FileCard in ChatSDK config

**What problem does this feature solve? (这个功能解决了什么问题)**
ChatSDK中通过config配置快速展现一个FileCard

**Describe the solution you'd like (描述您想要的解决方案)**
use a part of config like
```js
{
type: 'card',
content: {
code: 'file',
// .. some other FileCard props
},
}
```
in `box.config.messages` array to display a card such as :
https://chatui.io/components/file-card

**What does the proposed API look like? (你期望的 API 是怎样的)**
配置式的

Start by tracing how ChatSDK reads box.config.messages and how the FileCard component is exposed in the ChatUI documentation. Compare the requested card configuration with the existing message types and determine the required API and rendering path. Done means a configured FileCard appears from the messages array and the behavior is covered by the project's relevant tests or demo.

Written by the indexing model from the issue text.