[Feature Request]: Added searxng interface to the chat page

### Self Checks

- [x] I have searched for existing issues [search for existing issues](https://github.com/infiniflow/ragflow/issues), including closed ones.
- [x] I confirm that I am using English to submit this report ([Language Policy](https://github.com/infiniflow/ragflow/issues/5910)).
- [x] Non-english title submitions will be closed directly ( 非英文标题的提交将会被直接关闭 ) ([Language Policy](https://github.com/infiniflow/ragflow/issues/5910)).
- [x] Please do not modify this template :) and fill in all the required fields.

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

```Markdown
Added searxng interface to the chat page
```

### Describe the feature you'd like

Added searxng interface to the chat page

### Describe implementation you've considered

_No response_

### Documentation, adoption, use case

```Markdown

```

### Additional information

_No response_

The issue only identifies a SearXNG interface for the chat page and names no files, entry points, or tests. Start by locating the chat page implementation and reviewing how existing search integrations are structured. Before coding, clarify the SearXNG behavior, configuration, UI scope, and acceptance criteria; done should include a defined integration and corresponding tests.

Written by the indexing model from the issue text.