Starts the frontend. It loads the stylesheets and the interface's language, sends the first request of the page the visit lands on, then mounts App on index.html's #root.

A deploy renames every chunk, so a tab opened before it fails to load the lazy chunks it hasn't fetched yet. It then reloads to pick up the new build, but at most once a minute, so a chunk that's really missing shows its error instead of reloading forever.