fix(nginx): /product/ 路径转发给 Flutter Web，修复扫码跳转营销页问题

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

deploy/nginx-jiu.conf

@@ -39,6 +39,20 @@ server {
         try_files $uri $uri/ /app/index.html;
     }
 
+    # index.html 不缓存，确保每次发版后浏览器加载最新版
+    location = /app/index.html {
+        alias /opt/jiu/web/index.html;
+        add_header Cache-Control "no-cache, no-store, must-revalidate";
+        add_header Pragma "no-cache";
+        expires 0;
+    }
+
+    # 公开商品详情页（扫码跳转）→ 交给 Flutter Web 路由处理
+    location ~ ^/product/ {
+        root /opt/jiu/web;
+        try_files $uri /app/index.html;
+    }
+
     # 扫码页（/scan/<id> → scan.html，JS 从 URL 读取 id）
     location /scan/ {
         root /opt/jiu/marketing;