test: update tests for multi-language translation support

- Update marketplace_product_fixtures to create translations
- Update test_marketplace_product.py for translation-based titles
- Update test_product.py for effective property tests
- Update test_order.py to use get_title() method
- Add comprehensive CSV processor tests for translations
- Update stats service tests for new flat response structure
- Fix product schema tests with required marketplace_product_id field
- Add helper function create_marketplace_product_with_translation()

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tests/unit/models/schema/test_product.py

@@ -157,12 +157,13 @@ class TestProductResponseSchema:
             "vendor_id": 1,
             "marketplace_product": {
                 "id": 1,
+                "marketplace_product_id": "TEST001",  # Required field
                 "gtin": "1234567890123",
                 "title": "Test Product",
                 "description": "A test product",
                 "brand": "Test Brand",
-                "category": "Electronics",
-                "image_url": "https://example.com/image.jpg",
+                "google_product_category": "Electronics",
+                "image_link": "https://example.com/image.jpg",
                 "created_at": datetime.now(),
                 "updated_at": datetime.now(),
             },
@@ -194,12 +195,13 @@ class TestProductResponseSchema:
             "vendor_id": 1,
             "marketplace_product": {
                 "id": 1,
+                "marketplace_product_id": "TEST002",  # Required field
                 "gtin": "1234567890123",
                 "title": "Test Product",
                 "description": None,
                 "brand": None,
-                "category": None,
-                "image_url": None,
+                "google_product_category": None,
+                "image_link": None,
                 "created_at": datetime.now(),
                 "updated_at": datetime.now(),
             },