feat(SEO): enhance product and category JSON-LD with shipping and return policy details

- Added merchant return policy and shipping details to the JSON-LD for both product and category schemas.
- Updated delivery method price to reflect the new shipping rate of 5.90 €.
- Improved localization files to include loading messages for products and updated various translations for consistency.

src/i18n/locales/zh/product.js

@@ -13,7 +13,7 @@ export default {
   "weeks": "周",
   "arriving": "到货时间：",
   "inclVatFooter": "含 {{vat}}% 增值税,*",
-  "availability": "可用性",
+  "availability": "库存情况",
   "inStock": "有库存",
   "comingSoon": "即将上市",
   "deliveryTime": "交货时间",
@@ -25,6 +25,7 @@ export default {
   "pickupPrice": "自提价：每个插枝19.90欧元。",
   "consistsOf": "包含：",
   "loadingComponentDetails": "{{index}}. 正在加载组件详情...",
+  "loadingProduct": "产品正在加载...",
   "individualPriceTotal": "单件总价：",
   "setPrice": "套装价格：",
   "yourSavings": "您的节省：",