Add release smoke-check script stub

[karust]

Context

Release validation is currently manual. A small smoke-check script would make it easier and less error-prone to verify a build before publishing.

Scope

Add a script under scripts/ (e.g. scripts/smoke-check.sh) that builds the binary, starts the server, polls /health until ready (with a timeout), then shuts down and exits cleanly. Docker and go install checks can be follow-up work.

Done when

• The script fails fast with a useful, non-zero exit when the server does not become healthy.
• It is documented in docs/CONTRIBUTING.md (or a short scripts/README.md).
• Works from a clean checkout via make build followed by the script.

Contributor notes

Keep the first version small and source-build focused. The /health endpoint already exists in the server.

[arinbalyan]

Hi! I'd like to add the release smoke-check script stub. Will submit a PR soon.