feat(core): add core module with mixins, services, and background jobs

- Add Model Mixins: TimestampMixin, SoftDeleteMixin, AuditMixin, etc.
- Add Base Services: BaseService, BulkOperationsMixin, QueryOptimizerMixin
- Add Base ViewSets with bulk operations
- Add BackgroundJob model for Celery task tracking
- Add BaseAppCommand for management commands
- Add permissions, pagination, filters, cache, logging
- Migrate tests to factory_boy + faker
- Add CHANGELOG.md
- 297 tests passing

src/apps/user/urls.py

@@ -3,6 +3,8 @@ from rest_framework_simplejwt.views import TokenVerifyView
 
 from . import views
 
+app_name = "user"
+
 urlpatterns = [
     # Аутентификация
     path("register/", views.RegisterView.as_view(), name="register"),