Root and app layouts for the SquatchMail dashboard.
root/1 is the outermost HTML document (used as the LiveView
:root_layout) and is responsible for loading the dashboard's
self-contained CSS/JS bundle (see SquatchMail.Web.AssetController). It
intentionally does not inherit the host application's own root layout —
the dashboard is meant to look identical no matter which app embeds it,
the same way LiveDashboard and Oban Web render inside their own document
shell rather than the host's.
app/1 is the inner chrome every dashboard page renders through: the
220px sidebar (logo, nav, session easter egg) plus the main content slot.