Lets a deployment set what the app can't know from the browser: the style a visitor sees before choosing one, whether the server sends email, without which the digest settings do nothing, and which ways federated sign-in goes.
The server writes GERBEUR_DEFAULT_STYLE into index.html's default-style
<meta> tag, whether GERBEUR_SMTPS_URL is set into email-enabled, and
FEDERATION (api/config.ts) into federation-incoming and
federation-outgoing (api/lib/index-html.ts, and the Vite config in
development). index.html's
inline theme script reads the first one too.
The instance's style, which applies until a visitor or their account picks
one. A missing or unknown value means BASE_STYLE. ThemeProvider reads it.
Whether the server sends email. Without it the settings page shows the digest switches disabled, with a note why.
Whether users of other instances sign in here. Without it the login and register pages offer no other instance.
Whether this instance's users sign in to other instances. Without it the settings page doesn't list the instances they signed in to, since none remain.
Usage
import * as mod from "src/config/instance.ts";