[Feature]: 增强搜索功能

[qingchunnh]

Affected area

Frontend / UI

Problem or use case

当前搜索功能只显示最近8个对话，而且缺少内容预览和正文搜索，查找历史对话非常不便

Proposed behavior

1.初始加载的对话应该增加一些，允许向下滚动加载更多对话
2.在搜索界面可以直接预览对话内容
3.支持搜索消息正文
感觉此功能最好的参考还是openwebui🥲

Alternatives considered

No response

Compatibility, deployment, or migration impact

No response

Documentation or API contract impact

No response

Pre-submit checklist

• I searched existing issues and pull requests.
• This request is focused on one feature or improvement.
• I described user-facing, API, configuration, or deployment impact where relevant.