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.

backend/fleet/src/Fleet.Rpc/FleetMethods.cs

@@ -15,6 +15,31 @@ public static class FleetMethods
     public const string Revoked = "fleet.revoked";
 }
 
+/// <summary>
+/// 框架自己的方法声明，两个平面各一份。认证和握手阶段由连接代码直接处理的（<c>Inline</c>）不经过路由器。
+/// 同一个方法名在两个平面里可以有不同的发起方：<c>fleet.state.sync</c> 在节点面是服务端发给节点，在对等面是 Agent 发给 Probe。
+/// </summary>
+public static class FleetMethodTable
+{
+    public static readonly MethodTable Table = new(
+    [
+        // 节点面
+        MethodSpec.Notification(FleetMethods.Challenge, RpcSide.Server).AsInline(),
+        MethodSpec.Request(FleetMethods.Auth, RpcSide.Node).AsInline(),
+        MethodSpec.Request(FleetMethods.Hello, RpcSide.Node).AsInline(),
+        MethodSpec.Notification(FleetMethods.Heartbeat, RpcSide.Node).AsInline(),
+        MethodSpec.Request(FleetMethods.StateSync, RpcSide.Server),
+        MethodSpec.Notification(FleetMethods.OutboxAck, RpcSide.Server),
+        MethodSpec.Notification(FleetMethods.Revoked, RpcSide.Server),
+
+        // 对等面
+        MethodSpec.Notification(PeerMethods.Challenge, RpcSide.Listener).AsInline(),
+        MethodSpec.Request(PeerMethods.Auth, RpcSide.Dialer).AsInline(),
+        MethodSpec.Request(FleetMethods.StateSync, RpcSide.Listener),
+        MethodSpec.Notification(FleetMethods.OutboxAck, RpcSide.Listener),
+    ]);
+}
+
 /// <summary>二进制通道：0–15 保留给框架，产品从 16 开始。</summary>
 public static class FleetChannels
 {