feat(auditlog): real ClusterClient-based site audit push client

src/ScadaLink.AuditLog/ServiceCollectionExtensions.cs

@@ -121,11 +121,14 @@ public static class ServiceCollectionExtensions
             logger: sp.GetRequiredService<ILogger<FallbackAuditWriter>>(),
             filter: sp.GetRequiredService<IAuditPayloadFilter>()));
 
-        // ISiteStreamAuditClient: NoOp default. M6's reconciliation work brings
-        // the real gRPC-backed implementation (no site→central gRPC channel
-        // exists today — sites talk to central via Akka ClusterClient only).
-        // Bundle H's integration test substitutes a stub directly into the
-        // SiteAuditTelemetryActor's Props.Create call.
+        // ISiteStreamAuditClient: NoOp default. This binding remains correct for
+        // central/test composition roots that have no SiteCommunicationActor.
+        // The real implementation is ClusterClientSiteAuditClient, which pushes
+        // audit telemetry to central over Akka ClusterClient via the site's
+        // SiteCommunicationActor — the Host wires it directly into the
+        // SiteAuditTelemetryActor's Props.Create call for site roles (it cannot
+        // be a DI singleton because it needs the SiteCommunicationActor IActorRef,
+        // created during Akka bootstrap, not at DI-composition time).
         services.AddSingleton<ISiteStreamAuditClient, NoOpSiteStreamAuditClient>();
 
         // M3 Bundle F: site-side dual emitter for cached-call lifecycle