Issue #4: add structured logging and metrics foundation

src/MxGateway.Tests/Gateway/GatewayApplicationTests.cs

@@ -1,6 +1,8 @@
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Routing;
+using Microsoft.Extensions.DependencyInjection;
 using MxGateway.Server;
+using MxGateway.Server.Metrics;
 
 namespace MxGateway.Tests.Gateway;
 
@@ -19,4 +21,14 @@ public sealed class GatewayApplicationTests
 
         Assert.Equal("LiveHealth", endpoint.Metadata.GetMetadata<IEndpointNameMetadata>()?.EndpointName);
     }
+
+    [Fact]
+    public void Build_RegistersGatewayMetrics()
+    {
+        WebApplication app = GatewayApplication.Build([]);
+
+        GatewayMetrics metrics = app.Services.GetRequiredService<GatewayMetrics>();
+
+        Assert.NotNull(metrics);
+    }
 }