Every declared setting, grouped, with its effective value and where that value came from.
Read-only by design. Settings resolve once at boot — most of them configure
things Phoenix, Ecto and Nebulex read a single time — so an editable field
here would promise a change it could not deliver. What this page does
guarantee is that the list is complete: it renders Gamend.Settings.all/0,
the same declaration that generates .env.example and derives every
environment variable name — every one of them, without exception.
Variables that other software reads (RELEASE_COOKIE, FLY_REGION) are not
settings and are deliberately absent; the Config page reports those.