Refactor to use IHttpClientFactory and remove ApiOptions

Replaced direct injection of HttpClient with IHttpClientFactory
across the codebase to improve HTTP client management and align
with best practices. Removed dependency on ApiOptions and
IOptions<ApiOptions> in multiple services, simplifying constructors
and reducing configuration complexity.

Updated FontLoader to use IHttpClientFactory for font loading
with relative paths. Adjusted comments and documentation to
reflect these changes. Cleaned up unused using directives
related to ApiOptions.

EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/AuthService.cs

@@ -1,8 +1,6 @@
 using System.Net;
 using System.Net.Http;
 using System.Net.Http.Json;
-using EnvelopeGenerator.Server.Client.Options;
-using Microsoft.Extensions.Options;
 
 namespace EnvelopeGenerator.Server.Client.Services;
 
@@ -10,9 +8,8 @@ public enum EnvelopeLoginResult { Success, InvalidCode, NotFound, Error }
 
 public enum SenderLoginResult { Success, InvalidCredentials, Error }
 
-public class AuthService(IHttpClientFactory httpClientFactory, IOptions<ApiOptions> apiOptions)
+public class AuthService(IHttpClientFactory httpClientFactory)
 {
-    private readonly ApiOptions _api = apiOptions.Value;
 
     /// <summary>
     /// Checks whether the current user holds a valid receiver token for the given envelope key.