* Added `prf_enabled` and `prf_salt` columns to the `passkeys` table.
* Updated registration API endpoints to request and store the PRF extension capability and generate a secure salt.
* Updated the login API endpoints to map stored PRF salts into the `evalByCredential` array for the WebAuthn challenge.
* Enhanced the client-side WebAuthn SDK (`auth-client.js`) to extract the PRF Base64URL string output, decode it into a `Uint8Array`, and securely derive a 256-bit AES-GCM Key Encryption Key (KEK) via `crypto.subtle.deriveKey` using the `auth-yes:prf:device-share:v1` info string.
* Implemented graceful fallbacks throughout the stack to ensure registration and standard logins proceed if PRF is unsupported.
* Added corresponding unit tests to verify PRF flow and rejection logic.
* Verified visual and functional changes for the optional username input on the login page via Playwright scripts.
Co-authored-by: mrteye <1945243+mrteye@users.noreply.github.com>
