[Feature] webchat hang when meet long conversation

[findNextStep]

Feature Description

不太确定是否应当成为feature，先挂feature的位置了

我发现astrbot的webchat会一次性拉取所有的对话内容，当对话内容很长（做小说或者角色扮演）的时候，上下文长了加载会很慢，并且我看了一下请求似乎思考内容也是直接一次性下载的。

思考内容可能做惰性加载，只有点开的时候才请求，然后对话内容能让web端控制分页或者分批加载吗。

Use Case

No response

Checklist

• I have searched the Issue list for related features and confirmed this feature idea has never been proposed.
• The feature I am suggesting is related to AstrBot itself, not to a specific plugin.
• I have read and agree to the project's Code of Conduct.
• (Optional) I am willing to submit a PR to help implement this feature.