refactor: chat invoke & chat api

[Ricbet]

Types

• 🪚 Refactors

Background or solution

重构 Chat 模块以及 Chat 相关的后端接口定义

1. 将“默认对话”与 agent chat 整合，现在只会存在 agent chat
2. 初始会有一个以 Default_Chat_Agent_ 开头的唯一 id，承载之前“默认对话”的能力，见 chat-proxy.service.ts
3. Default_Chat_Agent 用户不感知，所以不会出现在 @ 符号的 agent 列表里
4. 调整流式对话内容的前后端交互方式，现在后端能直接返回一个 ChatReadableStream，直接往 ChatReadableStream 推送消息即可，删除了原先 this.client.onmessage 的调用方式
5. 调整 IAIBackService 接口的 requestStream 方法定义，现在需要返回一个 ChatReadableStream

Changelog

[railway-app]

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[codecov]

Codecov Report

Attention: Patch coverage is 17.34694% with 81 lines in your changes are missing coverage. Please review.

Project coverage is 56.10%. Comparing base (6e5234e) to head (0994254).
Report is 3 commits behind head on main.

Files	Patch %	Lines
...s/ai-native/src/browser/chat/chat-proxy.service.ts	0.00%	40 Missing and 3 partials ⚠️
...ai-native/src/browser/model/msg-history-manager.ts	0.00%	7 Missing ⚠️
...native/src/browser/chat/chat-agent.view.service.ts	0.00%	6 Missing ⚠️
...ges/ai-native/src/browser/chat/chat.api.service.ts	0.00%	6 Missing ⚠️
...kages/core-node/src/ai-native/base-back.service.ts	37.50%	5 Missing ⚠️
...i-native/src/browser/chat/chat.feature.registry.ts	0.00%	3 Missing and 1 partial ⚠️
...ai-native/src/browser/chat/chat-manager.service.ts	0.00%	2 Missing ⚠️
packages/ai-native/src/browser/chat/chat-model.ts	75.00%	2 Missing ⚠️
...i-native/src/browser/chat/chat.internal.service.ts	0.00%	2 Missing ⚠️
packages/ai-native/src/browser/index.ts	0.00%	2 Missing ⚠️
... and 2 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3630      +/-   ##
==========================================
- Coverage   56.10%   56.10%   -0.01%     
==========================================
  Files        1513     1514       +1     
  Lines       91785    91834      +49     
  Branches    18818    18817       -1     
==========================================
+ Hits        51498    51521      +23     
- Misses      33410    33437      +27     
+ Partials     6877     6876       -1     

Flag	Coverage Δ
jsdom	51.52% <16.32%> (-0.01%)	⬇️
node	15.65% <7.14%> (-0.01%)	⬇️

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[erha19]

LGTM