Chirag7026/opencode-quick-bill ? reverse-engineered prompt

Build me a simple Flutter app for quick billing and point of sale on mobile. I want a clean home screen where I can add products, choose quantities, see the running total, and finish a sale fast without a lot of taps. It should let me search or browse items, build a cart, apply a discount if needed, calculate tax if that makes sense, and show a neat receipt or invoice summary after checkout. I also want a basic history view for past bills so I can look them up later. Keep the design simple, fast, and easy to use on a phone. Use local storage if you need to so the app still works offline. Make the code organized and ready to run as a standard Flutter project, and please add a few basic tests too. If you need to check current Flutter docs for anything, feel free to look them up online.