Mobile sidebar

See https://github.com/dbernheisel/bernheisel.com/blob/main/lib/bern_web/templates/layout/nav.html.heex and Livebeats for examples. There should be a mobile version that is only shown with the smaller screen sizes and a desktop version.

The flyout from Livebeats is likely the approach I really want versus trying to style a completely different look and feel.