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/core/config.py

@@ -55,6 +55,13 @@ class Settings(BaseSettings):
     first_admin_password: str = ""
     first_admin_name: str = "Администратор"
 
+    # --- CRM ---
+    crm_base_url: str = "https://optstore.exocrm.com/api/1.1/"
+    crm_api_key: str = ""
+    crm_secret_key: str = ""
+    crm_shop_key: str = ""
+    crm_sid: int = 1
+
     @property
     def cors_origins(self) -> list[str]:
         """Список разрешённых origin'ов из строки через запятую."""