Add an opt-in latin prop to PriceInput (en-US grouping, English digits) and
use it for the discount-value and payment-amount fields on PaymentStep, which
were raw number inputs. Amounts now show 3-digit comma grouping and Persian
digits typed are converted to English (via PriceInput's toEnglishDigits).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>