Add using directives and update CreateAsync method

- Added `System.ComponentModel` and `System.ComponentModel.DataAnnotations.Schema` using directives for enhanced data annotation support.
- Applied the `[NonAction]` attribute to the `CreateAsync` method to prevent it from being treated as an action method by the ASP.NET MVC framework.

EnvelopeGenerator.GeneratorAPI/Controllers/EnvelopeController.cs

@@ -6,6 +6,8 @@ using MediatR;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;
 using Newtonsoft.Json;
+using System.ComponentModel;
+using System.ComponentModel.DataAnnotations.Schema;
 
 namespace EnvelopeGenerator.GeneratorAPI.Controllers;
 
@@ -99,6 +101,7 @@ public class EnvelopeController : ControllerBase
     /// </summary>
     /// <param name="envelope"></param>
     /// <returns></returns>
+    [NonAction]
     [Authorize]
     [HttpPost]
     public async Task<IActionResult> CreateAsync([FromQuery] CreateEnvelopeCommand envelope)