feat: add Products navigation button to sidebar

- Added new "Products" navigation item in sidebar
- Links to /product page (product listing)
- "Assets" button now links to / (product detail page)
- Added i18n support for "products" label (EN: Products, ZH: 产品)

Navigation structure:
- Assets → / (Product detail page)
- Products → /product (Product listing page)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

locales/zh.json

@@ -1,6 +1,7 @@
 {
   "nav": {
     "assets": "资产",
+    "products": "产品",
     "alp": "ALP",
     "swap": "交换",
     "lending": "借贷",