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>

backend/app/schemas/orders.py

@@ -16,6 +16,7 @@ from pydantic import BaseModel, ConfigDict, Field, field_validator
 
 if TYPE_CHECKING:
     from app.db.models.order import Order
+    from app.db.models.receipt import Receipt
 
 
 class OrderGoodOut(BaseModel):
@@ -82,9 +83,14 @@ class OrderRowOut(BaseModel):
     np_status_code: str | None
     np_cod_amount: str | None
     np_payment_status: str | None
+    # Последний ЕТТН-чек по заказу (в т.ч. отменённый/неудачный — для показа причины).
+    receipt_id: str | None = None
+    receipt_status: str | None = None
+    receipt_error: str | None = None
+    receipt_prepayment: str | None = None
 
     @classmethod
-    def from_order(cls, order: Order) -> OrderRowOut:
+    def from_order(cls, order: Order, receipt: Receipt | None = None) -> OrderRowOut:
         return cls(
             id=order.id,
             create_date_time=order.create_date_time,
@@ -104,4 +110,10 @@ class OrderRowOut(BaseModel):
                 else None
             ),
             np_payment_status=order.np_payment_status,
+            receipt_id=str(receipt.id) if receipt else None,
+            receipt_status=receipt.status.value if receipt else None,
+            receipt_error=receipt.error if receipt else None,
+            receipt_prepayment=(
+                f"{receipt.prepayment_kopecks / 100:.2f}" if receipt else None
+            ),
         )