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/config/settings/base.py

@@ -11,6 +11,9 @@ from decouple import Config, RepositoryEnv
 # Build paths inside the project like this: BASE_DIR / 'subdir'.
 BASE_DIR = Path(__file__).resolve().parent.parent.parent
 
+# Application version
+APP_VERSION = "1.0.0"
+
 # Load environment variables
 ENV_FILE = BASE_DIR / ".env"
 if ENV_FILE.exists():
@@ -50,15 +53,18 @@ INSTALLED_APPS = [
     "django.contrib.staticfiles",
     # Third-party apps
     "rest_framework",
+    "django_filters",
     "corsheaders",
     "django_celery_beat",
     "django_celery_results",
     "drf_yasg",
     # Local apps
+    "apps.core",
     "apps.user",
 ]
 
 MIDDLEWARE = [
+    "apps.core.middleware.RequestIDMiddleware",
     "corsheaders.middleware.CorsMiddleware",
     "django.middleware.security.SecurityMiddleware",
     "django.contrib.sessions.middleware.SessionMiddleware",
@@ -104,6 +110,17 @@ DATABASES = {
     },
 }
 
+# Cache configuration
+CACHES = {
+    "default": {
+        "BACKEND": "django_redis.cache.RedisCache",
+        "LOCATION": get_env("REDIS_URL", "redis://localhost:6379/0"),
+        "OPTIONS": {
+            "CLIENT_CLASS": "django_redis.client.DefaultClient",
+        },
+    },
+}
+
 
 # Password validation
 AUTH_PASSWORD_VALIDATORS = [
@@ -152,12 +169,27 @@ REST_FRAMEWORK = {
     "DEFAULT_PERMISSION_CLASSES": [
         "rest_framework.permissions.IsAuthenticatedOrReadOnly",
     ],
-    "DEFAULT_PAGINATION_CLASS": "rest_framework.pagination.PageNumberPagination",
+    "DEFAULT_FILTER_BACKENDS": [
+        "django_filters.rest_framework.DjangoFilterBackend",
+        "rest_framework.filters.SearchFilter",
+        "rest_framework.filters.OrderingFilter",
+    ],
+    "DEFAULT_PAGINATION_CLASS": "apps.core.pagination.StandardPagination",
     "PAGE_SIZE": 20,
     "DEFAULT_RENDERER_CLASSES": [
         "rest_framework.renderers.JSONRenderer",
         "rest_framework.renderers.BrowsableAPIRenderer",
     ],
+    "EXCEPTION_HANDLER": "apps.core.exception_handler.custom_exception_handler",
+    # Rate limiting
+    "DEFAULT_THROTTLE_CLASSES": [
+        "rest_framework.throttling.AnonRateThrottle",
+        "rest_framework.throttling.UserRateThrottle",
+    ],
+    "DEFAULT_THROTTLE_RATES": {
+        "anon": "100/hour",
+        "user": "1000/hour",
+    },
 }
 
 # JWT settings
@@ -237,6 +269,3 @@ LOGGING = {
         },
     },
 }
-
-# Test runner configuration
-TEST_RUNNER = "config.custom_test_runner.CustomTestRunner"