Add HSTS + Permissions-Policy + the standard X-Frame/X-Content/Referrer set to
the contrib nginx (443 block) and caddy examples; fix the caddy SPA try_files
fallback (stray space). Generic (no homeserver-specific CSP). The real prod
config lives in the matrix repo. P6-4 trimmed to headers only — patch-package /
types-drift / build-config skipped (see LOTUS_TODO).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>