Add endpoints for culture detection and improve cookie parsing

Added two endpoints to TestLocalizerController for retrieving culture from Accept-Language and user cookies. Enhanced GetCulture extension to parse and return the actual culture string from cookies. Updated usings for new extension methods.

EnvelopeGenerator.Web/Controllers/Test/TestLocalizerController.cs

@@ -1,9 +1,12 @@
 using AngleSharp.Common;
 using DigitalData.Core.API;
 using EnvelopeGenerator.Application.Resources;
+using EnvelopeGenerator.Web.Extensions;
 using EnvelopeGenerator.Web.Models;
+using Microsoft.AspNetCore.Localization;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.Extensions.Localization;
+using System.Globalization;
 
 namespace EnvelopeGenerator.Web.Controllers.Test
 {
@@ -28,5 +31,14 @@ namespace EnvelopeGenerator.Web.Controllers.Test
 
         [HttpGet("culture")]
         public IActionResult GetCultures(string? lang = null) => lang is null ? Ok(_cultures) : Ok(_cultures[lang]);
+
+        [HttpGet("culture/accept-language")]
+        public IActionResult GetCultureByAcceptLanguage()
+            => HttpContext.GetCultureByAcceptLanguage()?.Name is string culture 
+            ? Ok(culture)
+            : NotFound();
+
+        [HttpGet("culture/user")]
+        public IActionResult GetUserCulture() => Request.Cookies.GetCulture() is string cult ? Ok(cult) : NotFound();
     }
 }