agent: unify listening and dialing with directed mutual measurements

Replace Probe with Agent across node runtime, Fleet contracts, backend state, API and storage. Report incoming sessions and outgoing link health through each Agent uplink, and retain directed link controls and retry.

Update protocol fixtures and end-to-end coverage for the unified model; accept requested cancellation during the Fleet timeout test cleanup.

backend/src/MoShiro.Backend.Application/Updates/ReleasePoller.cs

@@ -5,14 +5,14 @@ using MoShiro.Protocol;
 namespace MoShiro.Backend.Application;
 
 /// <summary>
-/// 定时去镜像仓库取各组件（Agent、Probe、Backend 自己）最新的签名清单：CI 把清单登记给面板那一步是尽力而为的（网络不通只警告），
+/// 定时去镜像仓库取各组件（Agent、Backend 自己）最新的签名清单：CI 把清单登记给面板那一步是尽力而为的（网络不通只警告），
 /// 面板自己也去仓库取，Backend 的更新通知和节点的更新建议就不依赖那一步。取回来的清单要用发布公钥验过签才登记。
 /// </summary>
 public sealed partial class ReleasePoller : BackgroundService
 {
     private static readonly TimeSpan s_startupDelay = TimeSpan.FromSeconds(20);
     private static readonly TimeSpan s_interval = TimeSpan.FromMinutes(5);
-    private static readonly string[] s_components = [NodeKinds.Agent, NodeKinds.Probe, ReleaseService.BackendComponent];
+    private static readonly string[] s_components = [ReleaseService.AgentComponent, ReleaseService.BackendComponent];
 
     private readonly ReleaseService _releases;
     private readonly TimeProvider _time;