chore: replace /etc/hosts change with RFC6761 localhost

[salzig]

As described in https://www.rfc-editor.org/rfc/rfc6761#section-6.3, anything "ending" with .localhost is considered localhost, so we can use http://$label.onruby.localhost:3000 for development purposes without changing /etc/hosts at all.

unless we want to develop with safari, which doesn't support this right now.