fix: correct service methods and add inventory schema model

Services:
- admin_service: Add source_url to import job response, fix vendor_name
  to use vendor.name relationship instead of vendor_name field
- marketplace_product_service: Include reserved_quantity and
  available_quantity in InventoryLocationResponse
- vendor_service: Fix _get_product_by_id_or_raise to use database ID
  (int) instead of marketplace_product_id (str)

Schema:
- Add InventorySummaryResponse model for marketplace product service

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

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

models/schema/inventory.py

@@ -88,3 +88,11 @@ class InventoryMessageResponse(BaseModel):
     """Simple message response for inventory operations."""
 
     message: str
+
+
+class InventorySummaryResponse(BaseModel):
+    """Inventory summary response for marketplace product service."""
+
+    gtin: str
+    total_quantity: int
+    locations: list[InventoryLocationResponse]