fix(nginx): fall through to Next.js for root path instead of 403

try_files with $uri/ causes Nginx to treat / as a directory and return
403 when no index.html exists in dist root. Use $uri/index.html so
static directory indexes still work while unmatched routes (including /)
fall through to the Next.js runtime.

nginx-static-production.conf

@@ -198,11 +198,12 @@ http {
         }
 
         # Next.js 静态导出的页面路由 + ISR/SSR 回源
-        # 1) 优先命中已构建的静态 HTML/资源
+        # 1) 优先命中已构建的静态 HTML/资源（含目录 index.html）
         # 2) 未命中时转交给 Next.js 运行时（ISR 首次渲染、Draft 预览、动态路由）
+        # 注意：不能用 $uri/ 兜底目录，否则根路径会因目录无 index.html 直接 403 而不是回源
         location / {
             limit_req zone=general burst=20 nodelay;
-            try_files $uri $uri.html $uri/ @nextjs;
+            try_files $uri $uri.html $uri/index.html @nextjs;
         }
 
         # ISR/SSR 回源 named location