Don't allow ordering accessories on their own when specified in DB

Title is self explanatory. Have a check in create_order for it
I can right now navigate to the page directly - we shouldn't support this either: https://flavortown.hackclub.com/shop/order?shop_item_id=11

<img width="1223" height="385" alt="Image" src="https://github.com/user-attachments/assets/2f863505-5891-4d01-955b-970789a922ab" />