Add Checkbox ETTN receipts for Nova Poshta COD waybills

Cashier creates an ETTN receipt in Checkbox bound to the TTN with payment
control; Checkbox fiscalizes it itself when the parcel is paid for.

- cash_registers (Fernet-encrypted license key / PIN) and receipts tables
- Checkbox HTTP client + stub (ETTN does not work on test registers)
- two-phase create via ARQ job, timeout reconciliation, cron status polling
- /receipts and /cash-registers API, audit records
- dashboard: per-order and bulk create, prepayment, cancel; cash registers page

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/features/orders/OrderDetailModal.tsx

@@ -1,6 +1,7 @@
 import { Modal } from '@/components/Modal'
 import '@/features/orders/OrderDetailModal.css'
 import type { Order } from '@/features/orders/types'
+import { RECEIPT_STATUS } from '@/features/receipts/types'
 
 interface OrderDetailModalProps {
   order: Order
@@ -105,6 +106,27 @@ export function OrderDetailModal({ order, onClose }: OrderDetailModalProps) {
           <span>{order.total_amount} ₴</span>
         </div>
 
+        {order.receipt_status && (
+          <div className="order-modal-meta">
+            <div>
+              <span className="order-modal-label">ЕТТН-чек Checkbox</span>
+              <span className={`orders-status orders-status--${RECEIPT_STATUS[order.receipt_status].tone}`}>
+                {RECEIPT_STATUS[order.receipt_status].label}
+              </span>
+            </div>
+            <div>
+              <span className="order-modal-label">Предоплата в чеке</span>
+              <span>{order.receipt_prepayment ? `${order.receipt_prepayment} ₴` : '—'}</span>
+            </div>
+            {order.receipt_error && (
+              <div>
+                <span className="order-modal-label">Ошибка</span>
+                <span>{order.receipt_error}</span>
+              </div>
+            )}
+          </div>
+        )}
+
         <div className="order-modal-actions">
           <button type="button" className="order-modal-close-btn" onClick={onClose}>
             Закрыть