fix: 修复POST请求数据序列化问题，用JSON.stringify

src/api/product.js

@@ -104,9 +104,9 @@ export default {
       uni.request({
         url: `${import.meta.env.VITE_API_BASE_URL}/products/categories/${categoryId}/attributes`,
         method: 'POST',
-        data: attrs,
+        data: JSON.stringify(attrs),
         header: {
-          'Content-Type': 'application/json',
+          'Content-Type': 'text/plain',
           'Authorization': token ? `Bearer ${token}` : '',
           'X-User-Role': role
         },