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/api/v1/router.py

@@ -2,9 +2,10 @@
 
 from fastapi import APIRouter
 
-from app.api.v1 import auth, health, users
+from app.api.v1 import auth, health, orders, users
 
 api_router = APIRouter()
 api_router.include_router(health.router)
 api_router.include_router(auth.router)
 api_router.include_router(users.router)
+api_router.include_router(orders.router)