feat: add support for confirmation screen

[amitsingh05667]

Description

Adds support for the confirmation screen in both @auth0/auth0-acul-js and @auth0/auth0-acul-react.

This screen is shown when a user logs in with an identifier that has no existing account and the tenant is set up to auto-signup after OTP verification. Once the OTP is verified, the user lands on this confirmation screen to confirm or decline creating the account.

Changes

The only new behavior is the two actions on the screen instance:

import Confirmation from '@auth0/auth0-acul-js/confirmation';

const confirmation = new Confirmation();

// confirm and create the account
await confirmation.proceedToSignup();

// or decline and go back to login
await confirmation.goBack();

Same thing on the React side via the dedicated entry point:

import { proceedToSignup, goBack } from '@auth0/auth0-acul-react/confirmation';

await proceedToSignup(); // confirm
await goBack();          // cancel

Testing

Verified end-to-end using the sample app against a tenant with auto-signup enabled:

1. Logged in with an identifier that has no existing account.
2. Verified the OTP sent to that identifier.
3. Landed on the confirmation screen, which rendered the submitted identifier (read-only) along with Confirm and Cancel actions.
4. Confirm proceeds with account creation.
5. Cancel returns to the login screen without creating an account.

Confirmation2026.mov

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not the default branch