feat(scadabridge): add ScadaBridgeTelemetry meter + 4 instruments; register with OTel

src/ZB.MOM.WW.ScadaBridge.Host/SiteServiceRegistration.cs

@@ -2,6 +2,7 @@ using ZB.MOM.WW.ScadaBridge.AuditLog;
 using ZB.MOM.WW.ScadaBridge.ClusterInfrastructure;
 using ZB.MOM.WW.ScadaBridge.Communication;
 using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Services;
+using ZB.MOM.WW.ScadaBridge.Commons.Observability;
 using ZB.MOM.WW.ScadaBridge.DataConnectionLayer;
 using ZB.MOM.WW.ScadaBridge.ExternalSystemGateway;
 using ZB.MOM.WW.ScadaBridge.HealthMonitoring;
@@ -122,12 +123,14 @@ public static class SiteServiceRegistration
         // the always-on Prometheus exporter. Mount the /metrics scrape endpoint per role
         // with app.MapZbMetrics(). The same `?? "central"` SiteId default Program.cs uses
         // is applied here so the Resource attribute matches the log-enricher value.
-        // Meters left empty — application instruments are a deferred follow-on.
+        // The application meter is named so OTel observes its instruments; emit points are
+        // wired by follow-on tasks (the instruments are no-op until a listener attaches).
         services.AddZbTelemetry(o =>
         {
             o.ServiceName = "scadabridge";
             o.SiteId = config["ScadaBridge:Node:SiteId"] ?? "central";
             o.NodeRole = config["ScadaBridge:Node:Role"];
+            o.Meters = [ScadaBridgeTelemetry.MeterName];
         });
     }
 }