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/worker.py

@@ -1,10 +1,14 @@
-"""ARQ worker: раз в минуту опрашивает Nova Poshta по заказам без чека.
+"""ARQ worker: опрос Nova Poshta и ЕТТН-чеки Checkbox.
 
 Запускается отдельным процессом: `arq app.worker.WorkerSettings`.
+- `create_ettn_receipt` — задача, которую ставит API после запроса кассира;
+- `poll_np_statuses` — раз в минуту статусы ТТН по заказам без чека;
+- `poll_receipts` — раз в минуту повтор зависших `pending` и статусы `created`-чеков.
 """
 
 from __future__ import annotations
 
+import uuid
 from typing import Any
 
 from arq import cron
@@ -13,6 +17,8 @@ from arq.connections import RedisSettings
 from app.core.config import settings
 from app.core.logging import configure_logging, get_logger
 from app.db.session import SessionFactory
+from app.services import receipts as receipts_service
+from app.services.checkbox.client import get_checkbox_client
 from app.services.nova_poshta.np_client import NpTrackingClient
 from app.services.orders import sync_np_statuses
 
@@ -22,6 +28,7 @@ log = get_logger(__name__)
 async def startup(ctx: dict[str, Any]) -> None:
     configure_logging()
     ctx["np_client"] = NpTrackingClient(settings)
+    ctx["checkbox_client"] = get_checkbox_client()
     log.info("worker_starting", environment=settings.environment)
 
 
@@ -31,7 +38,25 @@ async def poll_np_statuses(ctx: dict[str, Any]) -> None:
     log.info("np_statuses_polled")
 
 
+async def create_ettn_receipt(ctx: dict[str, Any], receipt_id: str) -> None:
+    async with SessionFactory() as session:
+        await receipts_service.create_ettn_for_receipt(
+            session, ctx["checkbox_client"], uuid.UUID(receipt_id)
+        )
+
+
+async def poll_receipts(ctx: dict[str, Any]) -> None:
+    async with SessionFactory() as session:
+        await receipts_service.retry_pending_receipts(session, ctx["checkbox_client"])
+        await receipts_service.sync_ettn_statuses(session, ctx["checkbox_client"])
+    log.info("receipts_polled")
+
+
 class WorkerSettings:
     redis_settings = RedisSettings.from_dsn(settings.redis_url)
     on_startup = startup
-    cron_jobs = [cron(poll_np_statuses, minute=set(range(60)), run_at_startup=True)]
+    functions = [create_ettn_receipt]
+    cron_jobs = [
+        cron(poll_np_statuses, minute=set(range(60)), run_at_startup=True),
+        cron(poll_receipts, minute=set(range(60)), second=30),
+    ]