feat(payment): add qrDescription/customerID fields, TTL-based QR polling

- CartPaymentRequest gains qrDescription (brandName > hostname > fallback
  text) and customerID (telegram id)
- QrCreateResponse gains qrTTL; polling window now derived from it
  (min 60s) instead of a fixed 3-minute/36-check cap
- PAYMENT_MAX_CHECKS replaced by PAYMENT_MIN_POLL_SECONDS

src/app/services/api.service.ts

@@ -30,6 +30,7 @@ export interface QrCreateResponse {
   status?: string;
   qrStatus?: string;
   qrExpirationDate?: string;
+  qrTTL?: number;
   payload?: string;
   Payload?: string;
   qrUrl?: string;
@@ -47,6 +48,8 @@ export interface CartPaymentRequest {
   redirectUrl: string;
   telegramUsername: string;
   paymentMethod: 'qr' | 'card';
+  qrDescription?: string;
+  customerID?: string;
   items: Array<{ itemID: number; price: number; name: string; quantity?: number; delivery?: DeliveryOption[] }>;
 }