PhantomShift/nekotatsu-mobile ? reverse-engineered prompt

Build me a simple Rust desktop and mobile app for converting Tachiyomi backups into something Kotatsu can read.

I want a clean GUI where the user can first download the sources and parsers lists, then choose a backup file and a save location, and tap a convert button to run the conversion. Please make the app feel usable even if the UI is pretty basic for now, since this is mainly a small utility. It should also have a settings screen where I can change the URL for the extension list if my Tachiyomi backup was made with something other than the default Keiyoshi list.

If you need to, look up the current docs for the tools involved so the app runs correctly. Keep the focus on the GUI and let the actual backup conversion logic stay separate. Also make it work on Android, and if it is easy, let it run as a desktop frontend too.