NEW-1: add_header in location /api block suppressed server-level security
headers (HSTS, CSP, X-Frame-Options, etc). Duplicate all security headers
into the /api block explicitly per nginx inheritance rules.
NEW-2: Add 0.0.0.0/8 to _BLOCKED_NETWORKS — on Linux 0.0.0.0 connects
to localhost, bypassing the existing loopback check.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>