feat: add Passkey and MyAccount API support

[cschetan77]

Summary

This PR adds support for the Passkey and MyAccount APIs to the auth0-angular SDK, exposing them as Observable-based clients on AuthService — consistent with how the existing mfa client is structured.

Passkey API (AuthService.passkey)

Wraps the passkey client from @auth0/auth0-spa-js. Both methods handle the full WebAuthn challenge-response flow internally:

• passkey.signup(options) — register a new user with a passkey credential
• passkey.login(options?) — authenticate an existing user via passkey assertion

Both methods call authState.refresh() on success so that isAuthenticated$ and user$ update automatically, consistent with other authentication flows in the SDK.

MyAccount API (AuthService.myAccount)

Wraps the myAccount client from @auth0/auth0-spa-js, providing Observable versions of all seven account management operations:

Method	Description
getFactors()	List factors and their enrollment status
getAuthenticationMethods(type?)	List the user's enrolled authentication methods
getAuthenticationMethod(id)	Get a single authentication method by ID
deleteAuthenticationMethod(id)	Delete an authentication method
updateAuthenticationMethod(id, data)	Update an authentication method (name, preferred phone method)
enrollmentChallenge(options)	Start enrollment (step 1 of 2)
enrollmentVerify(options)	Complete enrollment by verifying the challenge (step 2 of 2)

Other changes

• ObservablePasskeyApiClient and ObservableMyAccountApiClient interfaces added to interfaces.ts, following the ObservableMfaApiClient pattern
• All passkey and MyAccount error classes (PasskeyError, PasskeyRegisterError, PasskeyChallengeError, PasskeyGetTokenError, MyAccountApiError) and types re-exported from the public API surface
• @auth0/auth0-spa-js minimum version bumped to ^2.21.0 where these APIs were introduced

Test plan

• 31 new unit tests added to auth.service.spec.ts covering: correct delegation to the underlying SDK, expected return values, authState.refresh() called after passkey authentication, and error propagation for all methods
• All 115 tests in auth.service.spec.ts pass (npm test -- --testPathPattern=auth.service.spec)

Usage

import { inject } from '@angular/core';
import { AuthService } from '@auth0/auth0-angular';

const auth = inject(AuthService);

// Passkey login — isAuthenticated$ and user$ update automatically on success
auth.passkey.login().subscribe(tokens => console.log(tokens.access_token));

// List enrolled authentication methods
auth.myAccount.getAuthenticationMethods().subscribe(methods => console.log(methods));

// Enroll a new TOTP authenticator (two-step flow)
auth.myAccount.enrollmentChallenge({ type: 'totp' }).pipe(
  switchMap(challenge =>
    auth.myAccount.enrollmentVerify({
      type: 'totp',
      location: challenge.location,
      auth_session: challenge.auth_session,
      otp_code: userEnteredOtp,
    })
  )
).subscribe(authMethod => console.log('Enrolled:', authMethod));