johnuberbacher/invoice-generator ? reverse-engineered prompt

Build me a simple invoice generator web app that looks clean and works in the browser.

I want users to be able to add line items, enter item names, quantities, prices, tax rates, and discounts, then see the totals update right away. It should have a nice preview so they can review the invoice before exporting it, and a button to download the finished invoice as a PDF file. Make the layout feel polished and easy to use on desktop and mobile, with a Bootstrap style and a modern React interface.

If it helps, look up current docs online for anything needed to make the PDF export work smoothly. Also include a currency picker and make sure the tax and discount math is correct. Keep the experience straightforward, so someone can quickly create an invoice and save it without any confusion.