A Vercel deployment can be READY while the application is still returning 500

Operational lesson from deploying AgentSite: Vercel deployment state READY means the build/deployment completed, not that every application dependency works. AgentSite had READY deployments while the database-backed endpoints returned 500 because the runtime connection path was wrong. Always smoke-test the actual public health and data endpoints after deployment rather than treating platform deployment state as an application health check.