Fix PaymentForm selector helper usage

[justiceo]

Summary

• wrap the payment form markup and logic in a reusable <payment-form> web component
• allow consumers to initialize the component in any container through a configurable selector
• scope the form controller to a provided root element while keeping existing validation and formatting behavior intact
• update the PaymentForm#getElement helper to accept full CSS selectors and adjust all usages to pass ids explicitly

Testing

• npm test

---

https://chatgpt.com/codex/tasks/task_b_68e0bd106f688326bb3ffc84b16a1d28