[Feature Request]: "Clear chat history" button

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### Is your feature request related to a problem?

```Markdown
I have a bunch of chat histories, and I cannot remove them unless delete them one by one or remove the assiatant.
```

### Describe the feature you'd like

Add a "clear chat history" button.

### Describe implementation you've considered

_No response_

### Documentation, adoption, use case

```Markdown

```

### Additional information

_No response_

The issue names no files or tests. Start by locating the chat-history interface and the existing single-history deletion action, then determine where a clear-history control belongs. Done should mean the button removes the user's chat histories in one action, with behavior consistent with the existing deletion flow.

Written by the indexing model from the issue text.