feat(api): UDT-004 controller de roles + refactor validator UDT-003 a lookup dinamico

- RolesController /api/v1/roles CRUD admin-only: GET list, GET {codigo}, POST, PUT, DELETE (soft-delete con guard 409)
- ExceptionFilter: mapea RolNotFound (404), RolAlreadyExists (409), RolInUse (409)
- DI: registra 5 handlers de Roles (Application) y IRolRepository/RolRepository (Infrastructure)
- CreateUsuarioCommandValidator: reemplaza whitelist hardcoded por IRolRepository.ExistsActiveByCodigoAsync via MustAsync; constructor recibe (AuthOptions, IRolRepository)
- Tests: 202 verdes (173 application + 29 api). Nuevas: RolesEndpointTests (13 integration), CreateUsuarioCommandValidatorTests reescrito con NSubstitute mock, CreateUsuario_WithInactiveRol_Returns400 en Api.Tests
- Fix: ApiIntegration pasa de IClassFixture (N factories) a ICollectionFixture (1 factory shared) — evitaba ObjectDisposedException sobre RSABCrypt al compartir coleccion con multiples test classes
- tests/tests.runsettings: MaxCpuCount=1 para evitar race entre assemblies sobre SIGCM2_Test

tests/SIGCM2.Api.Tests/Auth/AuthControllerTests.cs

@@ -6,7 +6,7 @@ using SIGCM2.TestSupport;
 namespace SIGCM2.Api.Tests.Auth;
 
 [Collection("ApiIntegration")]
-public class AuthControllerTests : IClassFixture<TestWebAppFactory>
+public class AuthControllerTests
 {
     private readonly HttpClient _client;