feat(admin): comma-grouped Latin amounts on the session payment step

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>

assets/admin/components/ui/PriceInput.tsx

@@ -9,11 +9,13 @@ interface PriceInputProps {
   style?: React.CSSProperties;
   disabled?: boolean;
   min?: number;
+  /** نمایش ارقام لاتین با جداکنندهٔ کاما (پیش‌فرض: فارسی). */
+  latin?: boolean;
 }
 
-function formatDisplay(num: number): string {
+function formatDisplay(num: number, latin: boolean): string {
   if (num === 0) return '';
-  return new Intl.NumberFormat('fa-IR').format(num);
+  return new Intl.NumberFormat(latin ? 'en-US' : 'fa-IR').format(num);
 }
 
 export default function PriceInput({
@@ -24,18 +26,19 @@ export default function PriceInput({
   style,
   disabled,
   min = 0,
+  latin = false,
 }: PriceInputProps) {
-  const [display, setDisplay] = useState(() => (value !== '' && value > 0 ? formatDisplay(value) : ''));
+  const [display, setDisplay] = useState(() => (value !== '' && value > 0 ? formatDisplay(value, latin) : ''));
 
   useEffect(() => {
-    setDisplay(value !== '' && Number(value) > 0 ? formatDisplay(Number(value)) : '');
-  }, [value]);
+    setDisplay(value !== '' && Number(value) > 0 ? formatDisplay(Number(value), latin) : '');
+  }, [value, latin]);
 
   const handleChange = (e: React.ChangeEvent<HTMLInputElement>) => {
     const raw = toEnglishDigits(e.target.value).replace(/[^0-9]/g, '');
     const num = raw === '' ? 0 : Math.max(min, parseInt(raw, 10));
     onChange(num);
-    setDisplay(num > 0 ? formatDisplay(num) : '');
+    setDisplay(num > 0 ? formatDisplay(num, latin) : '');
   };
 
   return (