Adds a Content-Security-Policy header to both nginx `location /aiui/`
blocks whose connect-src is scoped to the AIUI path prefix, so AIUI's
own JavaScript is browser-prevented from issuing a same-origin fetch
to /rpc/v1 with the ambient session cookie. Explicitly rejects the
`sandbox` iframe attribute (allow-scripts + allow-same-origin is the
known escape; dropping allow-same-origin breaks AIUI's storage and
its origin-checked bridge) and records why in both the nginx comment
and a new comment above the Chat.vue iframe. Adds
referrerpolicy="no-referrer" to the iframe so a media URL or page path
never leaks upstream via Referer.
Also adds an explicit `location /aiui/api/openrouter/ { return 404; }`
to both server blocks, closing 13-02's Task 3 checkpoint finding
(operator-accepted deviation 2026-08-03): the relay was already
structurally gone but the SPA catch-all served 200/405 instead of 404.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
