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

tests/apps/core/test_openapi.py

@@ -0,0 +1,133 @@
+"""Tests for core OpenAPI utilities"""
+
+from apps.core.openapi import (
+    CommonParameters,
+    CommonResponses,
+    _get_status_description,
+    api_docs,
+    paginated_response,
+)
+from django.test import TestCase
+from drf_yasg import openapi
+from rest_framework import serializers
+
+
+class DummySerializer(serializers.Serializer):
+    """Dummy serializer for testing"""
+
+    id = serializers.IntegerField()
+    name = serializers.CharField()
+
+
+class ApiDocsDecoratorTest(TestCase):
+    """Tests for @api_docs decorator"""
+
+    def test_decorator_returns_function(self):
+        """Test decorator returns wrapped function"""
+
+        @api_docs(summary="Test endpoint")
+        def my_view(request):
+            pass
+
+        self.assertTrue(callable(my_view))
+
+    def test_decorator_preserves_function_name(self):
+        """Test decorator preserves original function name"""
+
+        @api_docs(summary="Test endpoint")
+        def my_view(request):
+            pass
+
+        self.assertEqual(my_view.__name__, "my_view")
+
+
+class GetStatusDescriptionTest(TestCase):
+    """Tests for _get_status_description function"""
+
+    def test_known_status_codes(self):
+        """Test known status codes return Russian descriptions"""
+        self.assertEqual(_get_status_description(200), "Успешный запрос")
+        self.assertEqual(_get_status_description(201), "Ресурс создан")
+        self.assertEqual(_get_status_description(400), "Некорректный запрос")
+        self.assertEqual(_get_status_description(401), "Не авторизован")
+        self.assertEqual(_get_status_description(403), "Доступ запрещён")
+        self.assertEqual(_get_status_description(404), "Ресурс не найден")
+        self.assertEqual(_get_status_description(500), "Внутренняя ошибка сервера")
+
+    def test_unknown_status_code(self):
+        """Test unknown status code returns generic description"""
+        result = _get_status_description(418)
+        self.assertEqual(result, "HTTP 418")
+
+
+class CommonResponsesTest(TestCase):
+    """Tests for CommonResponses class"""
+
+    def test_success_response_type(self):
+        """Test SUCCESS is an openapi.Response"""
+        self.assertIsInstance(CommonResponses.SUCCESS, openapi.Response)
+
+    def test_created_response_type(self):
+        """Test CREATED is an openapi.Response"""
+        self.assertIsInstance(CommonResponses.CREATED, openapi.Response)
+
+    def test_not_found_response_type(self):
+        """Test NOT_FOUND is an openapi.Response"""
+        self.assertIsInstance(CommonResponses.NOT_FOUND, openapi.Response)
+
+    def test_unauthorized_response_type(self):
+        """Test UNAUTHORIZED is an openapi.Response"""
+        self.assertIsInstance(CommonResponses.UNAUTHORIZED, openapi.Response)
+
+    def test_validation_error_response_type(self):
+        """Test VALIDATION_ERROR is an openapi.Response"""
+        self.assertIsInstance(CommonResponses.VALIDATION_ERROR, openapi.Response)
+
+    def test_server_error_response_type(self):
+        """Test SERVER_ERROR is an openapi.Response"""
+        self.assertIsInstance(CommonResponses.SERVER_ERROR, openapi.Response)
+
+
+class CommonParametersTest(TestCase):
+    """Tests for CommonParameters class"""
+
+    def test_page_parameter(self):
+        """Test PAGE parameter configuration"""
+        self.assertEqual(CommonParameters.PAGE.name, "page")
+        self.assertEqual(CommonParameters.PAGE.in_, openapi.IN_QUERY)
+        self.assertEqual(CommonParameters.PAGE.type, openapi.TYPE_INTEGER)
+
+    def test_page_size_parameter(self):
+        """Test PAGE_SIZE parameter configuration"""
+        self.assertEqual(CommonParameters.PAGE_SIZE.name, "page_size")
+        self.assertEqual(CommonParameters.PAGE_SIZE.in_, openapi.IN_QUERY)
+
+    def test_search_parameter(self):
+        """Test SEARCH parameter configuration"""
+        self.assertEqual(CommonParameters.SEARCH.name, "search")
+        self.assertEqual(CommonParameters.SEARCH.type, openapi.TYPE_STRING)
+
+    def test_ordering_parameter(self):
+        """Test ORDERING parameter configuration"""
+        self.assertEqual(CommonParameters.ORDERING.name, "ordering")
+        self.assertEqual(CommonParameters.ORDERING.type, openapi.TYPE_STRING)
+
+    def test_id_parameter(self):
+        """Test ID parameter configuration"""
+        self.assertEqual(CommonParameters.ID.name, "id")
+        self.assertEqual(CommonParameters.ID.in_, openapi.IN_PATH)
+        self.assertTrue(CommonParameters.ID.required)
+
+
+class PaginatedResponseTest(TestCase):
+    """Tests for paginated_response function"""
+
+    def test_returns_response_object(self):
+        """Test function returns openapi.Response"""
+        result = paginated_response(DummySerializer)
+        self.assertIsInstance(result, openapi.Response)
+
+    def test_response_has_description(self):
+        """Test response has description"""
+        result = paginated_response(DummySerializer)
+        self.assertEqual(result.description, "Пагинированный список")