refactor(messaging): 拆分用户交互模块到 application/messaging 层

- 新增 application/messaging 交互层：router.py 统一会话优先级与回调分发，
  site/subscribe/skill/media/plugin 各交互状态与视图从 Chain 迁出
- MessageChain 改为通过 InteractionRouter 派发文本会话与按钮回调，
  新增结构化 callback_data 通道（兼容 CALLBACK: 文本前缀）
- Transfer 失败重试/AI 接管回调归入 TransferChain
- MediaInteractionChain 拆出为 app/chain/interaction.py（旧路径保留兼容别名）
- WebAgent Endpoint 去重，统一使用 agent.py 回调协议函数
- 删除 app/chain/skills.py（交互逻辑并入 SkillInteractionHandler）
- 同步更新架构文档与测试，全量 4476 通过

docs/rules/05-architecture.md

@@ -62,7 +62,7 @@ to make the directory tree look symmetrical.
 |---|---|
 | `app/application/*.py` | Audio, directory, downloader, filter, formatting, transfer history, image, media-server, notification, recognition, RSS, storage and torrent application services |
 | `app/application/site/` | Configured site catalog, authentication level and index-resource capability; the generated extension and its data bundle stay together here |
-| `app/application/messaging/` | Message rendering/routing, interactions and the Agent-to-message bridge |
+| `app/application/messaging/` | Message rendering/routing, interactions and the Agent-to-message bridge: `interaction.py` shared interaction contracts and view helpers; `router.py` unified interaction priority and callback dispatch; `site.py`/`subscribe.py`/`skill.py` per-command sessions, input parsing and views; `media.py` media interaction state while the business workflow stays in `MediaInteractionChain`; `plugin.py` plugin input capture and plugin button callbacks; `agent.py` agent choice state, callback protocol and WebAgent bridge; `message.py` notification rendering, templates and queue. Not a public SDK recommended for direct plugin use |
 | `app/application/security/` | Authentication, authorization, cookies, passkeys, OTP/two-factor, path/URL safety, SSRF and signing policy |
 
 Application services may use domain rules, runtime contracts, Oper classes and