Improve guidance for passkey implementations in Authentication Cheat …

[YK-03]

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Description

This PR improves the guidance in the FIDO2 / Passkeys section of the Authentication Cheat Sheet by recommending the use of well-maintained WebAuthn libraries or platform APIs instead of implementing authentication logic manually.

A reference link to the Web Authentication API (WebAuthn) documentation was also added to provide developers with an authoritative resource for implementing passkey-based authentication securely.

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[jmanico]

minor lint errors: cheatsheets/Authentication_Cheat_Sheet.md:350 MD012/no-multiple-blanks Multiple consecutive blank lines [Expected: 1; Actual: 2]