[FEATURE] auth - support passkey

## Is your feature request related to a problem?

Many companies are migrating from traditional MFA methods like TOTP to more secure methods, one of which is Passkey.

## Describe the solution you'd like

Allow users to log in using passkeys.

## Describe alternatives you've considered

TOTP.

## Use Case

Supporting passkey would make auth more secure - no reliance on passwords or traditional TOTP.

## Additional Context
Add any other context, mockups, or screenshots about the feature request here.

## Implementation Notes (Optional)

If using better-auth, there is an official plugin:

- https://better-auth.com/docs/plugins/passkey

## Related Issues

Linked with #784, #777

Start by reviewing related issues #784 and #777, then read the linked better-auth passkey plugin documentation. Establish the supported passkey login flow and acceptance criteria; the work is done when users can authenticate with passkeys alongside the existing authentication methods.

Written by the indexing model from the issue text.