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/agent/src/MoShiro.Agent/Tasks/TargetRunners.cs

@@ -127,7 +127,7 @@ public sealed class TargetRunners
         return IPAddress.TryParse(target, out address!);
     }
 
-    /// <summary>目标任务的行没有 Probe 一侧可以合并：积木交出的就是完整的行，Agent 自己盖章（目标、时钟锚点）并放进发件箱。</summary>
+    /// <summary>目标任务的行没有拨号方一侧可以合并：积木交出的就是完整的行，Agent 自己盖章（目标、时钟锚点）并放进发件箱。</summary>
     private sealed class LocalSink : IFragmentSink
     {
         private readonly TargetRunners _owner;
@@ -156,7 +156,7 @@ public sealed class TargetRunners
                 Port = port,
                 StartUtcMs = startUtcMs,
                 DurationMs = Math.Clamp(durationMs, 1, ChunkFinalizer.MaxDurationMs),
-                Clock = new ChunkClock { AgentMonoUs = anchor.AgentMonoUs, UtcMs = anchor.UtcMs, ProbeOffsetUs = 0 },
+                Clock = new ChunkClock { ListenerMonoUs = anchor.ListenerMonoUs, UtcMs = anchor.UtcMs, DialerOffsetUs = 0 },
             };
             _owner._chunks.Emit(new RawChunk(header, streams));
         }