更加炫酷的打字动画

### 需求动机

不知道可不可以在气泡打字的那个地方添加更加酷炫的打字效果，效果可以参考deerflow:https://github.com/bytedance/deer-flow, 和Google gemini对话框， 并且同时支持SSE和Restful，旧版的typing关键字在SSE情况下会失效

### 提议的 API 是什么样的？

_No response_

No file, test, or entry point is named. Start by locating the chat bubble typing-animation implementation and the SSE and REST message-handling paths, then compare their behavior with the DeerFlow and Google Gemini references. Done should include an agreed animation design that works with both transports and does not rely on the old typing keyword under SSE.

Written by the indexing model from the issue text.