feat(core, react): mfa step up components

[NaveenChand755]

Changes

Summary
Adds an MFA step-up challenge/enrollment UI that automatically triggers whenever any API call returns an mfa_required error.

What's new -

GateKeeper:

1. When a component’s API call triggers MFA, a dialog overlays the content.
2. Dismissing the dialog without completing MFA shows an error fallback with a retry option.

MFA Step-Up Components (packages/react/src/components/auth0/shared/mfa-step-up/):

MfaStepUp — Orchestrates the flow: list → enroll or challenge → complete.
AuthenticatorsList — Lets the user pick a factor to enroll or verify.
StepUpEnrollmentForm — Multi-step enrollment for OTP, Push, SMS, Voice, and Email.
StepUpVerifyForm — Handles OTP, OOB (SMS/Email/Voice), push, and recovery-code challenges.
StepUpCodeForm — Shared 6-digit OTP or recovery-code input.

New Hooks:

useMfaStepUp — Wraps enroll, challenge, and verify flows with loading state and error handling.
useMfaRequirements — Determines whether to show enrollment factors or active authenticators.

References

Testing

Please describe how this can be tested by reviewers. Be specific about anything not tested and reasons why. If this library has unit and tests should be added for new functionality and existing tests should complete without errors.

• This change adds unit test coverage
• This change has been tested on the latest version of the platform/language or why not

Checklist

• I have read the Auth0 general contribution guidelines
• I have read the Auth0 Code of Conduct
• All existing and new tests complete without errors