Fix System.Web Adapters service registration syntax in documentation (#36679)

* Fix SystemWebAdapters registration syntax in HttpApplicationHost


* Apply suggestion from @wadepickett

Updated the doc date.

---------

Co-authored-by: Vedika Gupta <vedikagupta@Vedikas-MacBook-Pro.local>
Co-authored-by: Wade Pickett <wpickett@microsoft.com>

Author: 3 people

aspnetcore/migration/fx-to-core/inc/remote-app-setup.md

@@ -5,7 +5,7 @@ author: wadepickett
 description: Remote app setup
 monikerRange: '>= aspnetcore-6.0'
 ms.author: wpickett
-ms.date: 12/10/2025
+ms.date: 01/26/2026
 ms.topic: concept-article
 uid: migration/fx-to-core/inc/remote-app-setup
 zone_pivot_groups: migration-remote-app-setup
@@ -64,7 +64,7 @@ To configure the application to be available to handle the requests from the ASP
     {
         HttpApplicationHost.RegisterHost(builder =>
         {
-            builder.AddSystemWebAdapters()
+            builder.Services.AddSystemWebAdapters()
                 .AddRemoteAppServer(options =>
                 {
                     // ApiKey is a string representing a GUID
@@ -266,7 +266,7 @@ To enable proxying from the ASP.NET Core application to the ASP.NET Framework ap
         HttpApplicationHost.RegisterHost(builder =>
         {
             builder.AddServiceDefaults();
-            builder.AddSystemWebAdapters();
+            builder.Services.AddSystemWebAdapters();
         });
     }
     ```