The container CMD ran `npm run start-docker`, i.e. `npm-run-all check-db
update-tracker start-server`. After the one-shot tasks exit, three Node VMs
stay resident for the container lifetime (npm -> npm-run-all -> npm ->
node server.js), each holding tens of MiB of anonymous memory for nothing.
Replace it with a small start script that runs the one-shot steps and then
`exec node server.js`, so the server becomes PID 1 and no launcher wrappers
remain. On a dev 3.2.0 build under realistic load the container RSS dropped
~28% (memory.stat anon 255 MiB -> 183 MiB); migrations still apply and
/api/heartbeat serves normally.
