feat(api): implement centralized exception handling for unified error responses

- Add custom_exception_handler to handle exceptions in a unified format
- Log errors with request context and provide debug information in development mode
- Update settings.py to use the new exception handler
- Export custom_exception_handler in __init__.py for accessibility

This enhances error management across the API, improving debugging and user experience.

backend/igny8_core/settings.py

@@ -204,6 +204,7 @@ REST_FRAMEWORK = {
         'igny8_core.api.authentication.CSRFExemptSessionAuthentication',  # Session auth without CSRF for API
         'rest_framework.authentication.BasicAuthentication',  # Enable basic auth as fallback
     ],
+    'EXCEPTION_HANDLER': 'igny8_core.api.exception_handlers.custom_exception_handler',  # Unified error format
 }
 
 # CORS Configuration