setup.py initialises auth.json and .env on a fresh install but was never
called by the Docker entrypoint, leaving new deployments without admin
credentials or a working config.
Adds a single gosu-wrapped call to setup.py before the final exec drop.
setup.py is fully idempotent (skips existing files) so subsequent starts
are unaffected. || true ensures a setup failure never blocks the app from
starting.
Fixes#1476