Add Next.js middleware.ts to apps/cms that applies all six security
headers on every response using the framework-agnostic
buildSecurityHeaders builder. No nonce is generated or forwarded —
the CMS is server-side only so CSP nonces are not required.
Includes a test suite mirroring the web-next pattern that asserts all
six headers are set, no x-nonce is emitted, and CSP mode switches
correctly between dev (unsafe-inline) and prod (strict-dynamic).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>