B-SPIN/ebay-label-maker ? reverse-engineered prompt

Build me a local first web app for processing eBay order CSV exports into printable thermal mailing labels.

I want to upload one or more order files, see them grouped into batches, and have the app automatically combine multiple orders from the same buyer going to the same address into one label so I can save on postage. It should let me optionally filter out tracked orders, flag address issues, and generate clean labels that include the item SKU and other shipping details in a simple, standardized layout.

Please make it feel polished and easy to use, with a dark mode, label size and font settings, and a print flow that works well for thermal printers like Dymo, Rollo, or Brother. Keep all data stored locally in the browser if possible, with no backend.

If it fits, add an Amazon export converter for Australia Post format and a basic invoice preview page too. Look up current docs online if you need to.