Nunito, the face the design is drawn in, as a variable TTF.

`web/public/fonts/` has the same family as woff2, which is right for a browser and
useless here: Slint cannot read woff2. This is the upstream variable TTF (weights
200-1000), which `SLINT_DEFAULT_FONT` is pointed at - by `shell.nix` for development,
and by the launcher `roles/pi_slint_frontend` installs on the device.

Nunito is licensed under the SIL Open Font License 1.1:
https://github.com/googlefonts/nunito