feat: add Create Product and CRUD actions to vendor-products page

- Add "Create Product" button in header
- Update actions column to View, Edit, Delete
- Add create/edit pages with forms and vendor selector
- Add POST/PATCH API endpoints for vendor products
- Add create_product and update_product service methods

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

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

app/services/vendor_product_service.py

@@ -238,6 +238,78 @@ class VendorProductService:
             else None,
         }
 
+    def create_product(self, db: Session, data: dict) -> Product:
+        """Create a new vendor product.
+
+        Args:
+            db: Database session
+            data: Product data dict
+
+        Returns:
+            Created Product instance
+        """
+        product = Product(
+            vendor_id=data["vendor_id"],
+            vendor_sku=data.get("vendor_sku"),
+            brand=data.get("brand"),
+            gtin=data.get("gtin"),
+            price=data.get("price"),
+            currency=data.get("currency", "EUR"),
+            availability=data.get("availability"),
+            is_active=data.get("is_active", True),
+            is_featured=data.get("is_featured", False),
+            is_digital=data.get("is_digital", False),
+            description=data.get("description"),
+        )
+
+        db.add(product)
+        db.flush()
+
+        logger.info(f"Created vendor product {product.id} for vendor {data['vendor_id']}")
+
+        return product
+
+    def update_product(self, db: Session, product_id: int, data: dict) -> Product:
+        """Update a vendor product.
+
+        Args:
+            db: Database session
+            product_id: Product ID to update
+            data: Fields to update
+
+        Returns:
+            Updated Product instance
+        """
+        product = db.query(Product).filter(Product.id == product_id).first()
+
+        if not product:
+            raise ProductNotFoundException(product_id)
+
+        # Update allowed fields
+        updatable_fields = [
+            "vendor_sku",
+            "brand",
+            "gtin",
+            "price_override",
+            "currency_override",
+            "availability",
+            "is_active",
+            "is_featured",
+            "is_digital",
+            "description",
+            "title",
+        ]
+
+        for field in updatable_fields:
+            if field in data:
+                setattr(product, field, data[field])
+
+        db.flush()
+
+        logger.info(f"Updated vendor product {product_id}")
+
+        return product
+
     def remove_product(self, db: Session, product_id: int) -> dict:
         """Remove a product from vendor catalog."""
         product = db.query(Product).filter(Product.id == product_id).first()
@@ -273,6 +345,9 @@ class VendorProductService:
             "brand": product.brand,
             "price": product.price,
             "currency": product.currency,
+            # Effective price/currency for UI (same as price/currency for now)
+            "effective_price": product.price,
+            "effective_currency": product.currency,
             "is_active": product.is_active,
             "is_featured": product.is_featured,
             "is_digital": product.is_digital,