Yinger/ts-excel-compare ? reverse-engineered prompt

Build me a simple web app that lets me compare two Excel spreadsheets side by side, kind of like those online text compare tools but for spreadsheet data.

I want a left panel for the original file and a right panel for the changed file. Let me either upload XLSX files or just paste table data directly into each side. After loading the files, automatically read the workbook, pick the first sheet by default, and give me a dropdown so I can switch sheets on each side if needed. Then add a clear Diff button that shows the differences in an easy to scan table with highlights for added and removed rows or cells, using markers like +++ for added and --- for removed.

It should feel clean and straightforward, with a polished UI and a spreadsheet style editing or viewing experience. If possible, include a way to copy the diff result so I can paste it back into Excel or another spreadsheet app. Look up current docs online if you need to.