Passkeys: Handle errors in passkey registration and auth flow

In the current passkey implementation most of the error cases are not handled. When it fails there should be some sort of visual feedback to let users know that something went wrong.

Start by locating the passkey registration and authentication flow in the iOS project and cataloging the unhandled failure cases. Done means each relevant failure provides users with clear visual feedback instead of failing silently.

Written by the indexing model from the issue text.