feat: declare every protocol method's direction and enforce it in the router; add the zero-trust design [CI]

Methods, roles and binary channels are declared in one table per plane (node and peer). RpcRouter checks direction, kind and role when handlers are registered, when messages arrive (fleet_protocol_violation, disconnect after repeated violations) and before sending. NodeConnection is split by responsibility.

README.md

@@ -97,6 +97,7 @@ Backend、Agent、Probe 以 OCI 镜像发布（Linux amd64、arm64），Agent
 | 文档 | 内容 |
 | --- | --- |
 | [`docs/architecture.md`](docs/architecture.md) | 架构、数据链路、安全边界、设计决策 |
+| [`docs/security.md`](docs/security.md) | 零信任设计稿（尚未实现）：威胁模型、名册和操作员凭证、监听隐身、extension 授权 |
 | [`docs/protocol.md`](docs/protocol.md)、[`backend/fleet/README.md`](backend/fleet/README.md) | 线协议、Fleet 节点框架（身份、注册、连接） |
 | [`docs/enrollment.md`](docs/enrollment.md) | 注册、身份、Probe 与 Agent 的接入 |
 | [`docs/measurement.md`](docs/measurement.md)、[`docs/analysis.md`](docs/analysis.md) | 采集引擎与任务模型、分析层与指标 |