Retrieves the last MFA code generated for a phone number. The code is cached in-memory when PLAYWRIGHT_TEST_API_KEY is set. Use this after triggering an MFA SMS to get the OTP without email/SMS access. GET /account/test/playwright/mfa-last-code?appDomain=...&phoneNumber=... Headers: x-playwright-api-key: <your-api-key> Returns: { code: string, expiresAt: number }