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/StorageTests.cs

@@ -256,7 +256,7 @@ public sealed class StorageTests : IDisposable
     // ───────────────────────── 节点、令牌、设置、事件 ─────────────────────────
 
     private static NewNode Node(string id, string name, NodeStatus status = NodeStatus.Active, byte fill = 1) =>
-        new(new NodeId(id), name, status, new byte[] { fill, 2, 3 }, new byte[32], ["lab"], """{"k":1}""", "1.0", 1_000);
+        new(new NodeId(id), name, status, new byte[] { fill, 2, 3 }, new byte[32], ["lab"], """{"k":1}""", "1.0", 1_000, TlsPublicKey: new byte[] { fill, 2, 3 });
 
     [Fact]
     public async Task Agents_NamesAreUniqueAmongEstablishedNodes_PendingOnesMayRepeat()