docs+ui: backfill XML doc comments and finish dashboard layout pass

Adds missing <summary>/<param> XML docs across 99 server, worker, and test
files so CommentChecker reports zero issues (TreatWarningsAsErrors needs the
analyzer clean). Bundles in WIP dashboard work: NavSection extraction,
MainLayout/site.css/js styling alignment, and DashboardOptions/Auth tweaks.

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

@@ -102,6 +102,7 @@ public sealed class GatewayApplicationTests
         }
     }
 
+    /// <summary>Verifies that dashboard routes are registered at root when enabled.</summary>
     [Fact]
     public async Task Build_WhenDashboardEnabled_RegistersDashboardRoutesAtRoot()
     {
@@ -126,6 +127,7 @@ public sealed class GatewayApplicationTests
         }
     }
 
+    /// <summary>Verifies that dashboard routes are not mapped when disabled.</summary>
     [Fact]
     public async Task Build_WhenDashboardDisabled_DoesNotMapDashboardRoutes()
     {