修复静态资源发布后不生效: /umd/缓存策略从immutable改为no-cache

构建产物文件名不带内容哈希，一年免验证的缓存策略导致每次蓝绿发布后
浏览器和CDN都会继续吃旧版本，用户需要清缓存或开无痕窗口才能看到更新。
改为no-cache后浏览器/CDN每次都会带条件请求向源站确认，未变化时只是
一次很快的304，一旦文件真的变了会立刻拿到新内容，不再需要手动清缓存。

docker/nginx.conf

@@ -11,8 +11,11 @@ server {
         try_files $uri $uri/ /index.html;
     }
 
+    # Filenames here aren't content-hashed, so a long/immutable cache would keep
+    # serving a stale bundle after every deploy. Force revalidation instead:
+    # cheap 304s when unchanged, immediate pickup of new content when not.
     location /umd/ {
-        add_header Cache-Control "public, max-age=31536000, immutable";
+        add_header Cache-Control "no-cache";
     }
 
     location /img/ {