BR19-gh/online-store-billing-system ? reverse-engineered prompt

Build me a simple online store billing app that lets the owner log in, add products with prices and images, and manage promo codes that customers can apply at checkout.

I want a clean front end where customers can browse the store, see the bill update as they add items, and enter a promo code to reduce the total. Then they should be able to send the finished bill straight to the owner’s WhatsApp number.

The owner side should have a basic admin page for adding, editing, and deleting products and promo codes. Keep it looking decent on desktop and mobile with a simple Bootstrap style.

Use Flask on the backend and a database so the products and promo codes persist. If you need to look up current docs online for anything, go ahead. Make sure the app runs locally and is easy to set up.