Convert Auth module to MediatR command

Adds the MediatR package and wires AddMediatR in DI. Replaces
IAuthService/AuthService with LoginCommand/LoginHandler, the pattern
the remaining modules will follow.

mws.api/Controllers/AuthController.cs

@@ -1,3 +1,4 @@
+using MediatR;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;
 using Mws.Application.Auth;
@@ -7,12 +8,12 @@ namespace Mws.Api.Controllers;
 [ApiController]
 [Route("api/auth")]
 [AllowAnonymous]
-public class AuthController(IAuthService authService) : ControllerBase
+public class AuthController(ISender sender) : ControllerBase
 {
     [HttpPost("login")]
     public async Task<ActionResult<LoginResponse>> Login([FromBody] LoginRequest request, CancellationToken ct)
     {
-        var response = await authService.LoginAsync(request, ct);
+        var response = await sender.Send(new LoginCommand(request), ct);
         return Ok(response);
     }
-}
+}