Implement the WebAuthn Signal API to synchronize server-side passkey revocations to platform passkey providers

Steps

1. The WebAuthn Signal API allows relying parties to signal to the platform (browser/OS) that a passkey has been revoked or that a credential is unknown, so the platform can update its passkey store.
2. Call PublicKeyCredential.signalUnknownCredential({ rpId, credentialId }) when the server receives an authentication attempt for a credential ID that no longer exists in your database; this hints to the platform to remove it from the passkey picker.
3. Call PublicKeyCredential.signalAllAcceptedCredentials({ rpId, userId, allAcceptedCredentialIds }) after a successful authentication to inform the platform of the complete set of valid credential IDs for this user, allowing the platform to remove stale entries.
4. Call PublicKeyCredential.signalCurrentUserDetails({ rpId, userId, name, displayName }) to update the display name or username stored in the passkey manager when the user changes their account details.
5. These calls are best-effort signals — the platform is not required to act on them immediately or at all; do not rely on them for security enforcement, only for UX cleanup.