verify-build-works

Smoke-test that the project still builds, the dev server starts, and the main user flow loads after a change. Run after every non-trivial edit, after a rollback (rollback-safe), after a fix from bug-triage-agent, before a commit, before pushing, and as part of release-check. Also when the user says "ainda tá funcionando?", "roda aí pra ver", "testa se não quebrou", "tá de pé?".