[Feature]: 代码块支持折叠

## Summary

输出代码块应该支持折叠，可以显著提升输出浏览体验。

## Component(s) Affected

- [ ] Core / Backend (app, agents, config, providers, utils, local_models)
- [ x ] Console (frontend web UI)
- [ ] Channels (DingTalk, Feishu, QQ, Discord, iMessage, etc.)
- [ ] Skills
- [ ] CLI
- [ ] Documentation (website)
- [ ] Tests
- [ ] CI/CD
- [ ] Scripts / Deploy

## Problem / Motivation

对于大段代码输出和代码文字混合输出，代码块折叠可以显著减少上下滑动量，显著提高浏览阅读体验。

## Proposed Solution

代码块应该显示少于固定行数（如5行）的内容，多余的部分折叠显示。

## Alternatives Considered

[Any other approaches or workarounds you thought about.]

## Additional Context

可以在下载按钮旁边加入一个折叠/展开按钮：

## Willing to Contribute

- [ ] I am willing to open a PR for this feature (after discussion).