The "AUTH_TYPE=oidc requires OIDC_ISSUER, OIDC_CLIENT_ID and
OIDC_FRONTEND_URL" check lived in app.py, so it only ran when the Flask
app was imported; a worker or script with the same misconfiguration
started fine. It is now a model validator on the auth group and runs
wherever Settings is loaded, with the same message.
DEPLOYMENT_TYPE, which app.py read straight from the environment to
decide whether a missing JWT_SECRET_KEY is fatal, is a documented
setting on the server group now, so it shows up in the reference like
every other variable the app reads.