Backend is bound to 127.0.0.1 — only nginx can reach it.
Nginx checks cookie_session presence. Adding backend auth broke
the LND UI iframe fetch because the session validation was too
strict for the cross-proxy cookie flow. The nginx layer is the
correct auth gate for this endpoint.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>