Add health check endpoint and refactor integration response handling

- Introduced a new public health check endpoint at `api/ping/` to verify API responsiveness.
- Refactored integration response handling to utilize a unified success and error response format across various methods in `IntegrationSettingsViewSet`, improving consistency and clarity in API responses.
- Updated URL patterns to include the new ping endpoint and adjusted imports accordingly.

backend/igny8_core/settings.py

@@ -268,8 +268,12 @@ SPECTACULAR_SETTINGS = {
     
     ## Authentication
     All endpoints require JWT Bearer token authentication except:
+    - `GET /api/v1/system/ping/` - Health check endpoint
     - `POST /api/v1/auth/login/` - User login
     - `POST /api/v1/auth/register/` - User registration
+    - `GET /api/v1/auth/plans/` - List subscription plans
+    - `GET /api/v1/auth/industries/` - List industries
+    - `GET /api/v1/system/status/` - System status
     
     Include token in Authorization header:
     ```