Adds a production Docker image (node:20-alpine) and an `app` service in
docker-compose.yml so the Next.js app can run as a long-lived container
instead of just build/test in ephemeral containers. Requires `apk add
openssl` before `npm ci`, otherwise Prisma silently picks the wrong query
engine binary on Alpine and only fails at runtime. Also wires
AUTH_TRUST_HOST=true, required by Auth.js when running behind the NPM
reverse proxy.
Co-Authored-By: Claude Sonnet 5 <[email protected]>
