Refactor: centralize HTTP client naming with Constants

Introduced a Constants class to define a unique HttpClientName for HTTP client registration and usage. Updated DependencyInjection and InvokeRecActionCommandHandler to use this centralized name, improving consistency and reducing risk of name collisions.

src/ReC.Application/DependencyInjection.cs

@@ -2,6 +2,7 @@
 using MediatR;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
+using ReC.Application.Common;
 using ReC.Application.Common.Behaviors;
 using ReC.Application.Common.Options;
 using System.Reflection;
@@ -35,7 +36,7 @@ public static class DependencyInjection
             cfg.LicenseKey = configOpt.LuckyPennySoftwareLicenseKey;
         });
 
-        services.AddHttpClient("Default")
+        services.AddHttpClient(Constants.HttpClientName)
             .ConfigurePrimaryHttpMessageHandler(() => new HttpClientHandler
             {
                 UseDefaultCredentials = false