Add security headers integration test

[collinsadi]

Security headers may be dropped by hosting CDN misconfiguration.

Add deployed URL fetch test asserting HSTS, X-Frame-Options, and Referrer-Policy headers.

Acceptance criteria:

• Test runs against staging URL.
• Missing headers fail CI.
• Hosting docs list required headers.

[ndyugwu]

@ndyugwu has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

i would like to work on this kindly assign me

ℹ️ Repo Maintainers: To accept this application, review their application or assign @ndyugwu to this issue.

[Usmanbalogun044]

@Usmanbalogun044 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello, Maintainer I can Resolve this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Usmanbalogun044 to this issue.