HSTS (Strict-Transport-Security) is now opt-in via FORCE_HTTPS=true.
Without it enabled, no HSTS header is sent — safe for dev environments
and enterprise deployments behind HTTP-only proxies without HTTPS certs.
When FORCE_HTTPS=true, sends 'max-age=31536000; includeSubDomains'.
Enterprise recommendation: set HSTS at nginx/ingress level instead.
.env.example documents the risk: enabling without certs breaks site access.