fix(sitecallaudit): correct stale relay docs and clarify ack switch

src/ScadaLink.Host/Actors/AkkaHostedService.cs

@@ -415,9 +415,11 @@ akka {{
         // and NotificationOutbox patterns. M3's dual-write transaction routes
         // SiteCalls upserts through AuditLogIngestActor's own scope-per-message
         // ISiteCallAuditRepository resolution, so this singleton is not on the
-        // M3 happy-path hot path; it exists so future direct-write callers
-        // (reconciliation puller, central→site Retry/Discard relay, KPI
-        // projector) Ask through a stable cluster proxy without further wiring.
+        // M3 happy-path hot path; it exists so direct-write callers Ask through
+        // a stable cluster proxy without further wiring. The central→site
+        // Retry/Discard relay now lives in this actor (see the
+        // RegisterCentralCommunication wiring below); the reconciliation puller
+        // is the remaining deferred direct-write caller.
         // Like AuditLogIngestActor, the actor takes the root IServiceProvider
         // and creates a fresh scope per message because ISiteCallAuditRepository
         // is a scoped EF Core service.