- Bind backend, frontend and mongo-express to 127.0.0.1; nginx on the host
proxies to them.
- Stop publishing MongoDB (27017); services reach it over the compose network.
- Override the frontend healthcheck to use 127.0.0.1 (nginx listens on IPv4
only, so localhost -> ::1 always failed).
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>