Point deploy.sh at /opt/gupi (its own dir + .env.prod) so it uploads, builds
on the server, migrates, and runs `docker compose -f
/opt/gupi/docker-compose.prod.yml --env-file /opt/gupi/.env.prod up -d`.
The app-only prod stack still joins the shared network and uses gu_common's
Postgres/MinIO. Adds .env.prod.example as the fill-in template.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
