refactor: reorganize tests into admin and vendor subdirectories

Split integration tests into logical admin/ and vendor/ subdirectories
for better organization. Updated fixture imports and test structure.

🤖 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

@@ -21,12 +21,12 @@ class TestProductCreateSchema:
         """Test valid product creation data."""
         product = ProductCreate(
             marketplace_product_id=1,
-            product_id="SKU-001",
+            vendor_sku="SKU-001",
             price=99.99,
             currency="EUR",
         )
         assert product.marketplace_product_id == 1
-        assert product.product_id == "SKU-001"
+        assert product.vendor_sku == "SKU-001"
         assert product.price == 99.99
 
     def test_marketplace_product_id_required(self):
@@ -93,7 +93,7 @@ class TestProductCreateSchema:
         """Test product with all optional fields."""
         product = ProductCreate(
             marketplace_product_id=1,
-            product_id="SKU-001",
+            vendor_sku="SKU-001",
             price=100.00,
             sale_price=80.00,
             currency="EUR",
@@ -119,7 +119,7 @@ class TestProductUpdateSchema:
         """Test partial update with only some fields."""
         update = ProductUpdate(price=150.00)
         assert update.price == 150.00
-        assert update.product_id is None
+        assert update.vendor_sku is None
         assert update.is_active is None
 
     def test_empty_update_is_valid(self):
@@ -167,7 +167,7 @@ class TestProductResponseSchema:
                 "created_at": datetime.now(),
                 "updated_at": datetime.now(),
             },
-            "product_id": "SKU-001",
+            "vendor_sku": "SKU-001",
             "price": 99.99,
             "sale_price": None,
             "currency": "EUR",
@@ -205,7 +205,7 @@ class TestProductResponseSchema:
                 "created_at": datetime.now(),
                 "updated_at": datetime.now(),
             },
-            "product_id": None,
+            "vendor_sku": None,
             "price": None,
             "sale_price": None,
             "currency": None,