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/MoShiroErrors.cs

@@ -13,9 +13,10 @@ public static class MoShiroErrors
     public static readonly ErrorCode SitePrivate = new("site_private");
     public static readonly ErrorCode NotFound = new("not_found");
     public static readonly ErrorCode AgentNotFound = new("agent_not_found");
-    public static readonly ErrorCode ProbeNotFound = new("probe_not_found");
-    public static readonly ErrorCode ProbeRevoked = new("probe_revoked");
-    public static readonly ErrorCode ProbeRequired = new("probe_required");
+    public static readonly ErrorCode NodeRevoked = new("node_revoked");
+    public static readonly ErrorCode DialerRequired = new("dialer_required");
+    public static readonly ErrorCode NotListening = new("not_listening");
+    public static readonly ErrorCode SelfLink = new("self_link");
     public static readonly ErrorCode TaskNotFound = new("task_not_found");
     public static readonly ErrorCode TestNotFound = new("test_not_found");
     public static readonly ErrorCode ChunkNotFound = new("chunk_not_found");
@@ -23,7 +24,7 @@ public static class MoShiroErrors
     public static readonly ErrorCode UnknownKind = new("unknown_kind");
     public static readonly ErrorCode UnknownPlan = new("unknown_plan");
     public static readonly ErrorCode NameConflict = new("name_conflict");
-    public static readonly ErrorCode ProbeOffline = new("probe_offline");
+    public static readonly ErrorCode DialerOffline = new("dialer_offline");
     public static readonly ErrorCode TestBusy = new("test_busy");
     public static readonly ErrorCode AgentNotActive = new("agent_not_active");
     public static readonly ErrorCode AgentOffline = new("agent_offline");