Browse, edit, upload, and delete files on the FAT32 image with mtools,
mirroring the wasm emulator's Files tab. Mutations stop the emulator
first because QEMU caches the card, so host writes to a live image would
be lost.
Split the emulator script into an xteink package so the CLI and the new
web UI share one QEMU driver. The web UI uploads firmware and an SD image,
boots them, drives the buttons, and long-polls the panel frame generation
so the screen updates on each e-ink refresh.
evan