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_response.py

@@ -0,0 +1,138 @@
+"""Tests for core response wrapper"""
+
+from apps.core.response import (
+    api_created_response,
+    api_error_response,
+    api_no_content_response,
+    api_paginated_response,
+    api_response,
+)
+from django.test import TestCase
+from rest_framework import status
+
+
+class APIResponseTest(TestCase):
+    """Tests for api_response function"""
+
+    def test_basic_response(self):
+        """Test basic successful response"""
+        response = api_response({"key": "value"})
+
+        self.assertEqual(response.status_code, status.HTTP_200_OK)
+        self.assertTrue(response.data["success"])
+        self.assertEqual(response.data["data"], {"key": "value"})
+        self.assertIsNone(response.data["errors"])
+
+    def test_response_with_request_id(self):
+        """Test response includes request ID in meta"""
+        response = api_response({"key": "value"}, request_id="test-id-123")
+
+        self.assertEqual(response.data["meta"]["request_id"], "test-id-123")
+
+    def test_response_with_custom_status(self):
+        """Test response with custom status code"""
+        response = api_response(None, status_code=status.HTTP_202_ACCEPTED)
+
+        self.assertEqual(response.status_code, status.HTTP_202_ACCEPTED)
+
+    def test_response_with_pagination(self):
+        """Test response includes pagination in meta"""
+        pagination = {"page": 1, "total": 100}
+        response = api_response([1, 2, 3], pagination=pagination)
+
+        self.assertEqual(response.data["meta"]["pagination"], pagination)
+
+
+class APIErrorResponseTest(TestCase):
+    """Tests for api_error_response function"""
+
+    def test_basic_error_response(self):
+        """Test basic error response"""
+        errors = [{"code": "test_error", "message": "Test error message"}]
+        response = api_error_response(errors)
+
+        self.assertEqual(response.status_code, status.HTTP_400_BAD_REQUEST)
+        self.assertFalse(response.data["success"])
+        self.assertIsNone(response.data["data"])
+        self.assertEqual(response.data["errors"], errors)
+
+    def test_error_response_with_custom_status(self):
+        """Test error response with custom status code"""
+        errors = [{"code": "not_found", "message": "Not found"}]
+        response = api_error_response(errors, status_code=status.HTTP_404_NOT_FOUND)
+
+        self.assertEqual(response.status_code, status.HTTP_404_NOT_FOUND)
+
+    def test_error_response_with_request_id(self):
+        """Test error response includes request ID"""
+        errors = [{"code": "error", "message": "Error"}]
+        response = api_error_response(errors, request_id="error-id-456")
+
+        self.assertEqual(response.data["meta"]["request_id"], "error-id-456")
+
+
+class APICreatedResponseTest(TestCase):
+    """Tests for api_created_response function"""
+
+    def test_created_response(self):
+        """Test 201 created response"""
+        response = api_created_response({"id": 1, "name": "New item"})
+
+        self.assertEqual(response.status_code, status.HTTP_201_CREATED)
+        self.assertTrue(response.data["success"])
+        self.assertEqual(response.data["data"]["id"], 1)
+
+
+class APINoContentResponseTest(TestCase):
+    """Tests for api_no_content_response function"""
+
+    def test_no_content_response(self):
+        """Test 204 no content response"""
+        response = api_no_content_response()
+
+        self.assertEqual(response.status_code, status.HTTP_204_NO_CONTENT)
+        self.assertTrue(response.data["success"])
+        self.assertIsNone(response.data["data"])
+
+
+class APIPaginatedResponseTest(TestCase):
+    """Tests for api_paginated_response function"""
+
+    def test_paginated_response(self):
+        """Test paginated response with correct metadata"""
+        data = [{"id": 1}, {"id": 2}]
+        response = api_paginated_response(
+            data, page=1, page_size=10, total_count=25
+        )
+
+        self.assertEqual(response.status_code, status.HTTP_200_OK)
+        self.assertEqual(response.data["data"], data)
+
+        pagination = response.data["meta"]["pagination"]
+        self.assertEqual(pagination["page"], 1)
+        self.assertEqual(pagination["page_size"], 10)
+        self.assertEqual(pagination["total_count"], 25)
+        self.assertEqual(pagination["total_pages"], 3)
+        self.assertTrue(pagination["has_next"])
+        self.assertFalse(pagination["has_previous"])
+
+    def test_paginated_response_last_page(self):
+        """Test paginated response on last page"""
+        response = api_paginated_response(
+            [{"id": 1}], page=3, page_size=10, total_count=25
+        )
+
+        pagination = response.data["meta"]["pagination"]
+        self.assertFalse(pagination["has_next"])
+        self.assertTrue(pagination["has_previous"])
+
+    def test_paginated_response_single_page(self):
+        """Test paginated response with single page"""
+        response = api_paginated_response(
+            [{"id": 1}], page=1, page_size=10, total_count=5
+        )
+
+        pagination = response.data["meta"]["pagination"]
+        self.assertEqual(pagination["total_pages"], 1)
+        self.assertFalse(pagination["has_next"])
+        self.assertFalse(pagination["has_previous"])