site/ is the website: a static page plus a worker that turns the newest
release of yetone/magpie-releases into an update feed (/api/latest, with
every file's SHA-256), stable download links and an install script.
The app asks the feed at start-up and every six hours, downloads a newer
version in the background, and installs it on Restart to Update or on
quit. A download must match its checksum and be signed by the same team
as the app it replaces. `magpie update` does the same from a terminal and
replaces a bare binary in place.