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/db/models/audit.py

@@ -31,6 +31,7 @@ class AuditAction(str):
     USER_CREATED = "user.created"
     USER_UPDATED = "user.updated"
     USER_DEACTIVATED = "user.deactivated"
+    ORDER_DELETED = "order.deleted"
 
 
 class AuditLog(UUIDPrimaryKeyMixin, Base):