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/tests/MoShiro.Backend.Tests/OwnerTests.cs

@@ -9,7 +9,7 @@ using MoShiro.Backend.Application;
 namespace MoShiro.Backend.Tests;
 
 /// <summary>
-/// 每个 Agent 和 Probe 都必须有属主（passkey）：属主是节点敏感内容（extension 会话、加密数据）绑定的人，装上时固定在节点本地。
+/// 每个 监听侧和拨号侧 Agent 都必须有属主（passkey）：属主是节点敏感内容（extension 会话、加密数据）绑定的人，装上时固定在节点本地。
 /// 没有信任根、没选属主、选了操作员集合之外的凭证，都不能创建加入码；安装脚本和容器入口缺了属主也不装。
 /// </summary>
 public sealed class OwnerPolicyTests
@@ -65,7 +65,7 @@ public sealed class OwnerEndToEndTests : IDisposable, IClassFixture<BackendFixtu
         Assert.Equal(HttpStatusCode.BadRequest, none.StatusCode);
         Assert.Contains("owner", await none.Content.ReadAsStringAsync(), StringComparison.Ordinal);
 
-        using HttpResponseMessage stranger = await session.PostAsync("/api/admin/join-tokens", BackendFixture.Json(new JsonObject { ["role"] = "probe", ["controllers"] = new JsonArray("not-an-operator") }));
+        using HttpResponseMessage stranger = await session.PostAsync("/api/admin/join-tokens", BackendFixture.Json(new JsonObject { ["role"] = "agent", ["controllers"] = new JsonArray("not-an-operator") }));
         Assert.Equal(HttpStatusCode.BadRequest, stranger.StatusCode);
 
         // 明确选了一把，或者不指定（默认是全部操作员）：可以，命令里带着创世指纹和属主
@@ -76,7 +76,7 @@ public sealed class OwnerEndToEndTests : IDisposable, IClassFixture<BackendFixtu
         Assert.Contains("MOSHIRO_CONTROLLERS=", linux, StringComparison.Ordinal);
         Assert.Contains(known, linux, StringComparison.Ordinal);
 
-        using HttpResponseMessage defaults = await session.PostAsync("/api/admin/join-tokens", BackendFixture.Json(new JsonObject { ["role"] = "probe" }));
+        using HttpResponseMessage defaults = await session.PostAsync("/api/admin/join-tokens", BackendFixture.Json(new JsonObject { ["role"] = "agent" }));
         Assert.Equal(HttpStatusCode.Created, defaults.StatusCode);
     }