fix(site-event-logging): resolve SiteEventLogging-006,009,011 — severity index, accurate XML doc, dead-placeholder removal

src/ScadaLink.SiteEventLogging/ServiceCollectionExtensions.cs

@@ -21,9 +21,9 @@ public static class ServiceCollectionExtensions
         return services;
     }
 
-    public static IServiceCollection AddSiteEventLoggingActors(this IServiceCollection services)
-    {
-        // Placeholder for Akka actor registration (Phase 4+)
-        return services;
-    }
+    // NOTE: EventLogHandlerActor is wired up directly in
+    // ScadaLink.Host/Actors/AkkaHostedService.cs as a cluster singleton, because the
+    // actor must be created inside the ActorSystem with the resolved
+    // IEventLogQueryService. There is intentionally no DI helper for that here — a
+    // former AddSiteEventLoggingActors placeholder was dead code and has been removed.
 }