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/README.md

@@ -38,7 +38,7 @@ dotnet publish src/MoShiro.Backend -c Release -r <RID> -p:PublishAot=true
 
 例如 `<RID>` 可为 `win-x64`、`linux-x64` 或 `linux-arm64`。NativeAOT 发布需要对应平台的 C/C++ 工具链。仓库根目录的 `scripts/publish.sh backend <RID>` 可构建单个平台的 Backend 可执行文件；容器发布由 Woodpecker tag 流水线完成，详见 [`../docs/ops/deployment.md`](../docs/ops/deployment.md)。
 
-正式发布通过 Woodpecker tag 流水线生成 Linux/amd64 与 Linux/arm64 OCI 镜像，容器内监听 `8080`，数据写入挂载的 `/data` 卷。Agent 与 Probe 的多平台二进制包单独发布，不包含在 Backend 镜像中。
+正式发布通过 Woodpecker tag 流水线生成 Linux/amd64 与 Linux/arm64 OCI 镜像，容器内监听 `8080`，数据写入挂载的 `/data` 卷。Agent 与 拨号方 的多平台二进制包单独发布，不包含在 Backend 镜像中。
 
 ## 本地运行