feat(scadabridge): wire AddZbTelemetry + /metrics in both composition roots

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

@@ -21,6 +21,7 @@ using ZB.MOM.WW.ScadaBridge.Security;
 using ZB.MOM.WW.ScadaBridge.SiteCallAudit;
 using ZB.MOM.WW.ScadaBridge.TemplateEngine;
 using ZB.MOM.WW.ScadaBridge.Transport;
+using ZB.MOM.WW.Telemetry;
 using Serilog;
 
 // SCADABRIDGE_CONFIG determines which role-specific config to load (Central or Site)
@@ -248,6 +249,12 @@ try
         // All three are anonymous and use the canonical ZbHealthWriter JSON output.
         app.MapZbHealth();
 
+        // Observability — mount the always-on Prometheus /metrics scrape endpoint.
+        // AddZbTelemetry (in SiteServiceRegistration.BindSharedOptions) wires the OTel
+        // Resource + standard instrumentation + Prometheus exporter; this exposes them.
+        // Requires endpoint routing (app.UseRouting() above).
+        app.MapZbMetrics();
+
         app.MapStaticAssets();
         app.MapCentralUI<ZB.MOM.WW.ScadaBridge.Host.Components.App>();
         app.MapInboundAPI();
@@ -304,6 +311,17 @@ try
 
         var app = builder.Build();
 
+        // Endpoint routing middleware. The gRPC service mapping below and the
+        // /metrics scrape endpoint both run on endpoint routing, so UseRouting()
+        // must be present before the Map* calls on the site role.
+        app.UseRouting();
+
+        // Observability — mount the always-on Prometheus /metrics scrape endpoint.
+        // AddZbTelemetry (in SiteServiceRegistration.Configure → BindSharedOptions)
+        // wires the OTel Resource + standard instrumentation + Prometheus exporter;
+        // this exposes them on the site node too.
+        app.MapZbMetrics();
+
         // Map gRPC service — resolves the singleton SiteStreamGrpcServer from DI
         app.MapGrpcService<ZB.MOM.WW.ScadaBridge.Communication.Grpc.SiteStreamGrpcServer>();