feat(health): SiteAuditTelemetryStalledTracker subscribes to EventStream (#23 M6)

src/ScadaLink.AuditLog/ServiceCollectionExtensions.cs

@@ -259,6 +259,17 @@ public static class ServiceCollectionExtensions
             .Bind(config.GetSection(PartitionMaintenanceSectionName));
         services.AddHostedService<AuditLogPartitionMaintenanceService>();
 
+        // M6 Bundle E (T7): central-singleton tracker for per-site
+        // SiteAuditTelemetryStalledChanged events published by
+        // SiteAuditReconciliationActor. Singleton so the EventStream
+        // subscription registers exactly once on host startup; the tracker's
+        // ctor needs an ActorSystem which is composed by the AkkaHostedService
+        // — we go through a factory so the SP is the source of truth for the
+        // system reference rather than re-resolving it on the consumer side.
+        services.AddSingleton<SiteAuditTelemetryStalledTracker>(sp =>
+            new SiteAuditTelemetryStalledTracker(
+                sp.GetRequiredService<Akka.Actor.ActorSystem>()));
+
         return services;
     }
 }