refactor(adminui): omit error key on success cert-audit rows + assert OccurredAtUtc (review)

tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Audit/CertAuditEventsTests.cs

@@ -26,6 +26,7 @@ public sealed class CertAuditEventsTests
         evt.Actor.ShouldBe("alice");
         evt.Outcome.ShouldBe(AuditOutcome.Success);
         evt.EventId.ShouldNotBe(Guid.Empty);
+        evt.OccurredAtUtc.ShouldBeGreaterThan(DateTimeOffset.UtcNow.AddSeconds(-5));
         evt.DetailsJson.ShouldNotBeNull();
         evt.DetailsJson!.ShouldContain(Thumb);
     }
@@ -88,13 +89,14 @@ public sealed class CertAuditEventsTests
         evt.DetailsJson!.ShouldContain("store write failed");
     }
 
-    /// <summary>On success the error text is omitted from the details payload (it serializes null).</summary>
+    /// <summary>On success the error text AND the error key are omitted from the details payload.</summary>
     [Fact]
     public void Build_success_omits_error_text()
     {
         var evt = CertAuditEvents.Build("Trust", "rejected", Thumb, "alice", success: true, error: "ignored");
 
         evt.DetailsJson!.ShouldNotContain("ignored");
+        evt.DetailsJson!.ShouldNotContain("error");
     }
 
     /// <summary>The public Category constant matches the value stamped onto built events.</summary>