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_middleware.py

@@ -0,0 +1,34 @@
+"""Tests for core middleware"""
+
+from django.urls import reverse
+from rest_framework.test import APITestCase
+
+
+class RequestIDMiddlewareTest(APITestCase):
+    """Tests for RequestIDMiddleware"""
+
+    def test_request_id_generated(self):
+        """Test that request ID is generated and returned in response header"""
+        url = reverse("core:health")
+        response = self.client.get(url)
+
+        self.assertIn("X-Request-ID", response)
+        self.assertIsNotNone(response["X-Request-ID"])
+        # UUID format check (36 chars with hyphens)
+        self.assertEqual(len(response["X-Request-ID"]), 36)
+
+    def test_request_id_passed_through(self):
+        """Test that provided X-Request-ID is passed through"""
+        url = reverse("core:health")
+        custom_id = "custom-request-id-12345"
+        response = self.client.get(url, HTTP_X_REQUEST_ID=custom_id)
+
+        self.assertEqual(response["X-Request-ID"], custom_id)
+
+    def test_different_requests_different_ids(self):
+        """Test that different requests get different IDs"""
+        url = reverse("core:health")
+        response1 = self.client.get(url)
+        response2 = self.client.get(url)
+
+        self.assertNotEqual(response1["X-Request-ID"], response2["X-Request-ID"])