Fixed fatal error in ShippingController.
Issue:
- ShippingController extended BaseController (does not exist)
- Caused PHP fatal error: Class not found
Fix:
- Changed to extend WP_REST_Controller (WordPress standard)
- Matches pattern used by PaymentsController and StoreController
- Added proper PHPDoc header
Result:
✅ API endpoint now works
✅ No more 500 errors
✅ Shipping zones load correctly