🛡️ Sentinel: security hardening of headers and admin guard

[bbaaxx]

🛡️ Sentinel: security hardening of headers and admin guard

💡 What:

• Refined admin guard path matching to prevent accidental matches (e.g., /administration).
• Added missing security headers: X-Permitted-Cross-Domain-Policies and X-DNS-Prefetch-Control.
• Hardened Permissions-Policy with additional restricted features (usb, interest-cohort, screen-wake-lock).

🎯 Why:

• Prevent potential bypass or accidental exposure of admin logic on non-admin paths.
• Defense in depth by restricting browser features and cross-domain policies.
• Compliance with security best practices for SvelteKit applications.

🧪 Verification:

• Updated src/hooks.server.security.spec.ts and verified all tests pass.
• Verified linting and formatting pass cleanly.
• Basic e2e connectivity verified.

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PR created automatically by Jules for task 8057860943100731105 started by @bbaaxx

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