refactor(notification): 建立通知渠道通用管理契约 channel_manage

- schemas 层新增 NotificationAction 公共动作词汇表（状态/二维码/退出/连通性/缓存迁移）
- 模块实现统一 channel_manage(channel, action, **params)，按渠道名路由，
  非本渠道返回 None；动作语义、表单参数解释与临时参数初始化封闭在模块内
- NotificationChain 收敛为单一 manage_channel 纯透明转发，
  chain 层不再出现任何渠道名与模块特色
- endpoint 路由路径保持前端兼容，内部统一走通用接口
- 新增 6 项契约守护测试，文档记录通用模式：新渠道接入无需改 chain

docs/rules/05-architecture.md

@@ -212,6 +212,15 @@ exceptions and value domains used by both modules and upper layers live in
 method names. The directory remains unchanged because discovery and plugin code
 depend on this established runtime root.
 
+Channels that need login management or temporary-parameter initialization
+follow one generic contract instead of per-channel APIs: modules implement
+`channel_manage(channel, action, **params)`, route by the requested
+`MessageChannel` (returning `None` for other channels), and interpret actions
+from the shared `schemas.types.NotificationAction` vocabulary plus opaque form
+parameters themselves. `NotificationChain.manage_channel` forwards transparently
+and must stay free of any channel-specific names or logic; new channels adopt
+the same contract without touching the chain.
+
 ### DB / Oper layer
 
 SQLAlchemy models stay under `app/db/models/`; the data access classes live in