Refactor HttpClient usage and NTLM auth handling

Centralize HttpClient configuration using IHttpClientFactory with a named "Default" client. Move NTLM authentication logic from HttpClientHandler to request-level options, improving testability and aligning with .NET best practices.

src/ReC.Application/DependencyInjection.cs

@@ -1,10 +1,10 @@
-using MediatR;
+using FluentValidation;
+using MediatR;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using ReC.Application.Common.Behaviors;
 using ReC.Application.Common.Options;
 using System.Reflection;
-using FluentValidation;
 
 namespace ReC.Application;
 
@@ -35,7 +35,11 @@ public static class DependencyInjection
             cfg.LicenseKey = configOpt.LuckyPennySoftwareLicenseKey;
         });
 
-        services.AddHttpClient();
+        services.AddHttpClient("Default")
+            .ConfigurePrimaryHttpMessageHandler(() => new HttpClientHandler
+            {
+                UseDefaultCredentials = false
+            });
 
         return services;
     }