fix(ml): add family_name field required for User Products model

- ML's new User Products model requires family_name in item body
- Use product name as family_name (generic product description)
- Keep title for backward compatibility with legacy sellers

pos/services/marketplace_external_service.py

@@ -173,8 +173,13 @@ def build_item_payload(
         shipping_payload["free_shipping"] = False
         shipping_payload["methods"] = []
         shipping_payload["costs"] = [{"description": "Envio", "cost": str(shipping_cost)}]
+    # family_name is required for ML's User Products model (enabled sellers).
+    # It's a generic product description shared across variations.
+    family_name = inventory_row.get("name") or title
+
     payload = {
         "title": title,
+        "family_name": family_name,
         "category_id": meli_category_id,
         "price": round(float(price), 2),
         "currency_id": "MXN",
@@ -185,6 +190,7 @@ def build_item_payload(
         "pictures": [{"source": url} for url in _resolve_image_urls(images, base_url) if url],
         "shipping": shipping_payload,
         "attributes": [],
+        "seller_custom_field": inventory_row.get("part_number") or str(inventory_row.get("id")),
     }
 
     # Collect extra attribute IDs to avoid duplicates