feat(site-call-audit): relay Retry/Discard emit operator-identity audit rows

Additive RequestedBy on Retry/DiscardSiteCallRequest, plumbed from the Central UI.
On an Applied relay, SiteCallAuditActor emits one best-effort CachedResolve central
direct-write row (Submitted/Discarded) with the operator as Actor. Gated on an
injected ICentralAuditWriter (null in existing tests → no mirror read, unchanged);
the site remains the source of truth for the state change.

src/ZB.MOM.WW.ScadaBridge.Commons/Messages/Audit/SiteCallRelayMessages.cs

@@ -58,10 +58,16 @@ public enum SiteCallRelayOutcome
 /// <param name="SourceSite">
 /// The owning site (<c>SiteCall.SourceSite</c>) the relay is routed to.
 /// </param>
+/// <param name="RequestedBy">
+/// The authenticated operator who initiated the retry, stamped as the <c>Actor</c>
+/// on the central direct-write audit row the relay emits — recording *who asked*
+/// (Task 14). Additive; null where no identity is available.
+/// </param>
 public sealed record RetrySiteCallRequest(
     string CorrelationId,
     Guid TrackedOperationId,
-    string SourceSite);
+    string SourceSite,
+    string? RequestedBy = null);
 
 /// <summary>
 /// Site Call Audit → Central UI: result of a <see cref="RetrySiteCallRequest"/>.
@@ -99,7 +105,8 @@ public sealed record RetrySiteCallResponse(
 public sealed record DiscardSiteCallRequest(
     string CorrelationId,
     Guid TrackedOperationId,
-    string SourceSite);
+    string SourceSite,
+    string? RequestedBy = null);
 
 /// <summary>
 /// Site Call Audit → Central UI: result of a <see cref="DiscardSiteCallRequest"/>.