fix: rename duplicate 'purchases' i18n key to 'purchaseCount'

The admin.landings namespace had two 'purchases' keys at the same level:
a string for purchase count label and an object for purchases section.
JSON last-key-wins caused the string to be overwritten by the object,
producing "returned an object instead of string" error on landings list.

src/locales/fa.json

@@ -2917,7 +2917,7 @@
       "metaDesc": "توضیحات متا",
       "active": "فعال",
       "inactive": "غیرفعال",
-      "purchases": "خرید",
+      "purchaseCount": "خرید",
       "copyUrl": "کپی URL",
       "urlCopied": "URL کپی شد",
       "deleteConfirm": "حذف صفحه فرود «{{title}}»؟",