ciguard: Web UI is missing HTTP defence-in-depth headers

Summary ciguard's FastAPI Web UI src/ciguard/web/app.py does not set HTTP defence-in-depth headers. OWASP ZAP baseline scan flagged 11 alerts: missing Content-Security-Policy Medium, X-Frame-Options Medium, Sub-Resource-Integrity on /api/docs Medium, COOP / COEP / CORP Low, Permissions-Policy Low...