When host is set to 0.0.0.0, the gateway now enforces that either token
or token_issue_secret must be configured — it refuses to start otherwise.
Bootstrap endpoint behavior:
- token_issue_secret configured: always validate regardless of source IP
(handles reverse-proxy scenarios where all connections appear as localhost)
- No secret: only localhost can bootstrap (local dev mode)
The frontend shows an authentication form when bootstrap returns 401/403,
persists the secret in localStorage, and retries automatically on reload.