Add a CI workflow to run the smoke tests on push/PR

[williamzujkowski]

Problem

The repo has no .github/workflows. Per the README, tests are only exercised weekly by the upstream ecosystem-smoke.yml in nexus-agents. There is no signal on a push or PR to this repo, so a schema/typecheck break can land on main unnoticed for up to a week.

Suggested fix

Add a minimal GitHub Actions workflow (Node >=22 per engines) that runs npm ci, npm run typecheck, and npm test on push and pull_request. This complements the upstream weekly run with per-change feedback.