Add CRM order queue: live sync, view modal, receipt tabs, delete

Wires the CRM (exoCRM GetOrders) into the dashboard as a locally
persisted order queue instead of the previous static mockup:

- CrmClient Protocol + ExoCrmClient/StubCrmClient for the CRM's
  signed JSON-RPC API
- Order model + migration, synced from CRM on each queue view;
  soft-deleted orders stay hidden across re-syncs
- GET/DELETE /api/v1/orders with "no receipt"/"receipt issued" tabs
  (the latter is empty until Checkbox fiscalization lands)
- Dashboard: real order list, item-detail modal, tab switcher,
  one-click delete

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/app/services/crm/client.py

@@ -0,0 +1,15 @@
+"""Protocol клиента CRM — позволяет подменять реализацию в тестах (`StubCrmClient`)."""
+
+from __future__ import annotations
+
+from typing import Protocol
+
+from app.schemas.orders import OrderOut
+
+
+class CrmError(Exception):
+    """CRM ответила `status: ERROR` (см. поле `errors` в ответе API)."""
+
+
+class CrmClient(Protocol):
+    async def get_orders(self, *, status: str) -> list[OrderOut]: ...