feat(mxgateway): adopt AddZbSerilog — MEL→Serilog provider swap (behaviour-preserving)

src/ZB.MOM.WW.MxGateway.Tests/Gateway/GatewayApplicationTests.cs

@@ -2,6 +2,7 @@ using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
 using ZB.MOM.WW.MxGateway.Server;
 using ZB.MOM.WW.MxGateway.Server.Dashboard;
@@ -29,6 +30,15 @@ public sealed class GatewayApplicationTests
         Assert.DoesNotContain("/health/live", paths);
     }
 
+    /// <summary>Verifies that Build registers Serilog as the host logging provider.</summary>
+    [Fact]
+    public void Build_UsesSerilogLoggerProvider()
+    {
+        using var app = GatewayApplication.Build([]);
+        var factory = app.Services.GetRequiredService<ILoggerFactory>();
+        Assert.Equal("SerilogLoggerFactory", factory.GetType().Name);
+    }
+
     /// <summary>Verifies that Build registers the gateway metrics service.</summary>
     [Fact]
     public async Task Build_RegistersGatewayMetrics()