feat: add MyAccount API client support

[yogeshchoudhary147]

The `myAccount` client introduced in auth0-spa-js#1615 was not yet surfaced through the React SDK. This PR exposes it so it is accessible via `useAuth0`.

Changes

`useAuth0().myAccount` (new)

Factors

• `getFactors()`: list all MFA factors enabled on the tenant with their `type` and `usage`

Authentication methods

• `getAuthenticationMethods(type?)`: list enrolled methods, optionally filtered by type
• `getAuthenticationMethod(id)`: get a single method by ID
• `updateAuthenticationMethod(id, data)`: update `name` or `preferred_authentication_method`
• `deleteAuthenticationMethod(id)`: remove an enrolled method

Enrollment (two-step)

• `enrollmentChallenge(options)`: initiate enrollment for any factor type; returns challenge data (WebAuthn creation options, barcode URI, recovery code, password policy, etc.)
• `enrollmentVerify(options)`: confirm enrollment; returns the created `AuthenticationMethod`

Supports: `passkey`, `webauthn-platform`, `webauthn-roaming`, `phone`, `email`, `totp`, `push-notification`, `recovery-code`, `password`.

Implementation pattern

`myAccount` follows the same pattern as `mfa` — a `useMemo(() => client.myAccount, [client])` passthrough. No `useCallback` wrappers or `GET_ACCESS_TOKEN_COMPLETE` dispatches are needed since none of these operations affect `isAuthenticated` or `user`.

Exports

`MyAccountApiClient` (type) and `MyAccountApiError` are now exported from the package root.

Dependency

Bumps `@auth0/auth0-spa-js` to `^2.21.1`.

Test plan

11 unit tests in `tests/my-account.test.tsx`. 128 tests passing overall, 100% coverage across all metrics (statements, branches, functions, lines).

Availability

• `myAccount` is defined on the context after mount
• All seven methods are present on the client

Methods

• `getFactors()`: resolves to an array
• `getAuthenticationMethods()`: resolves to an array
• `getAuthenticationMethods('passkey')`: type filter forwarded correctly
• `getAuthenticationMethod(id)`: resolves to correct method
• `updateAuthenticationMethod(id, data)`: resolves to updated method
• `deleteAuthenticationMethod(id)`: resolves without error
• `enrollmentChallenge(options)`: resolves with challenge shape (`id`, `auth_session`)
• `enrollmentVerify(options)`: resolves to created `AuthenticationMethod`

Error handling

• `MyAccountApiError` thrown by a method propagates untouched to the caller