Refactor services to use IHttpClientFactory

Refactored `DocReceiverElementService` and `EnvelopeService` to use `IHttpClientFactory` instead of directly injecting `HttpClient`, improving flexibility and testability.

Updated constructors to accept `IHttpClientFactory` and replaced direct `HttpClient` usage with named clients (`"EnvelopeGenerator.Server"`). Adjusted methods to use the factory-created clients for HTTP requests.

Added `using Microsoft.Extensions.Options;` in `Program.cs` and registered `EnvelopeService` and `DocReceiverElementService` in the dependency injection container for proper resolution. Clarified their usage in SSR scenarios with comments.

Removed redundant `using` directives and aligned imports with the updated implementation.

These changes enhance maintainability, scalability, and testability by leveraging `IHttpClientFactory` for better HTTP client management and dependency injection.

EnvelopeGenerator.Server/EnvelopeGenerator.Server/Program.cs

@@ -10,6 +10,7 @@ using EnvelopeGenerator.Domain.Constants;
 using Microsoft.AspNetCore.Authentication.Cookies;
 using Microsoft.AspNetCore.Localization;
 using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Options;
 using System.Globalization;
 using Scalar.AspNetCore;
 using Microsoft.OpenApi.Models;
@@ -318,6 +319,12 @@ try
     builder.Services.AddScoped<SignatureCacheService>();
     builder.Services.AddSingleton<AppVersionService>();
 
+    // EnvelopeService with HttpClient factory (for SSR scenarios)
+    builder.Services.AddScoped<EnvelopeService>();
+
+    // DocReceiverElementService (SignatureService alternative)
+    builder.Services.AddScoped<DocReceiverElementService>();
+
     // SSR Authentication Service (for Envelope Receiver pages)
     builder.Services.AddScoped<EnvelopeGenerator.Server.Services.IEnvelopeAuthService, EnvelopeGenerator.Server.Services.EnvelopeAuthService>();