Add totp api support with signup & oauth

[lakhansamani]

Feature Description

Currently TOTP API is added for login resolver.
We need to add same support for signup API, verify email API and oauth login apis
Describe the solution you'd like

Describe alternatives you've considered

Additional context

[lakhansamani]

Implemented — TOTP is available as an MFA factor during signup and the OAuth-return continuation, not just password login. Most recently reinforced in #686 (login.go now offers WebAuthn/TOTP consistently across signup, OAuth, and password paths).