Add store-item Excel export/import for bulk price and stock updates.

Dashboard can download grouped product variants and re-upload to update price and stock. Also expose Content-Disposition for downloads and keep related product/customer API docs in sync.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/website-api/openapi.json

@@ -449,7 +449,7 @@
         ],
         "responses": {
           "200": {
-            "description": "{ product }"
+            "description": "{ product, relatedProducts } — relatedProducts uses the product list-card shape (incl. store). Ranked by relativity (same category, then same brand) with availability beside it (in-stock first within each group). Up to 8 items; excludes the current product."
           }
         }
       }