feat(integrations): добавлена заготовка интеграции Recommerce

- Создана структура marketplaces/ для маркетплейсов
- Модели: MarketplaceIntegration, WooCommerceIntegration, RecommerceIntegration
- Сервисы: MarketplaceService, WooCommerceService, RecommerceService
- RecommerceService содержит методы для работы с API:
  - test_connection(), sync(), fetch_products()
  - push_product(), update_stock(), update_price()
- IntegrationConfig обновлён с новой интеграцией

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

myproject/integrations/services/marketplaces/__init__.py

@@ -0,0 +1,9 @@
+from .base import MarketplaceService
+from .woocommerce import WooCommerceService
+from .recommerce import RecommerceService
+
+__all__ = [
+    'MarketplaceService',
+    'WooCommerceService',
+    'RecommerceService',
+]