thanks @downtownallday
* this invalidates all user_keys after TOTP status is changed for user
* after changing TOTP state, a login is required
* due to the forced login, we can't and don't need to store the code used for setup in `mru_code`
* this allows implementation of other mfa schemes in the future (webauthn)
* also makes key management easier and enforces one totp credentials per user on db-level