feat: add marketplace products admin UI with copy-to-vendor functionality

- Add admin marketplace products page to browse imported products
- Add admin vendor products page to manage vendor catalog
- Add product detail pages for both marketplace and vendor products
- Implement copy-to-vendor API to copy marketplace products to vendor catalogs
- Add vendor product service with CRUD operations
- Update sidebar navigation with new product management links
- Add integration and unit tests for new endpoints and services

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

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

app/exceptions/product.py

@@ -15,9 +15,7 @@ class ProductNotFoundException(ResourceNotFoundException):
     """Raised when a product is not found in vendor catalog."""
 
     def __init__(self, product_id: int, vendor_id: int | None = None):
-        details = {"product_id": product_id}
         if vendor_id:
-            details["vendor_id"] = vendor_id
             message = f"Product with ID '{product_id}' not found in vendor {vendor_id} catalog"
         else:
             message = f"Product with ID '{product_id}' not found"
@@ -27,8 +25,11 @@ class ProductNotFoundException(ResourceNotFoundException):
             identifier=str(product_id),
             message=message,
             error_code="PRODUCT_NOT_FOUND",
-            details=details,
         )
+        # Add extra details after init
+        self.details["product_id"] = product_id
+        if vendor_id:
+            self.details["vendor_id"] = vendor_id
 
 
 class ProductAlreadyExistsException(ConflictException):