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/shared/MoShiro.Protocol/IpVersions.cs

@@ -8,6 +8,6 @@ public static class IpVersions
 
     public static bool IsValid(string? value) => value is V4 or V6;
 
-    public static string LineSeries(string probeId, string ipVersion) =>
-        RawChunkHeader.LinePrefix + probeId + (ipVersion == V6 ? ":ipv6" : "");
+    public static string LineSeries(string dialerId, string ipVersion) =>
+        RawChunkHeader.LinePrefix + dialerId + (ipVersion == V6 ? ":ipv6" : "");
 }