Product stock can become negative on page refresh

Description:
Currently, if a user adds a product to the cart and then refreshes the shop page, the stock quantity decreases again, which can result in negative stock values.

<img width="1529" height="573" alt="Image" src="https://github.com/user-attachments/assets/1b498f9b-5c23-4b20-b007-5f232fe4b38b" />