fix(ancpi): use form-data multipart for saveProductMetadataForBasketItem

Angular uses doPostAsFormMultipart — the save endpoint requires
multipart/form-data, not application/x-www-form-urlencoded.
Install form-data package and restore multipart upload.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

package.json

@@ -16,6 +16,7 @@
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "docx": "^9.6.0",
+    "form-data": "^4.0.5",
     "jspdf": "^4.2.0",
     "jszip": "^3.10.1",
     "lucide-react": "^0.564.0",