chore(web): finalize scroll behavior and preview assertions

reaction_board/web/static/router.js

@@ -82,7 +82,7 @@ async function render() {
       // 导航状态更新不应阻断页面渲染
     }
   }
-  window.scrollTo({ top: 0, behavior: "instant" });
+  window.scrollTo({ top: 0, behavior: "auto" });
   routeElement.innerHTML = `<div class="page-loading"><div class="skeleton skeleton-title"></div>
     <div class="skeleton skeleton-card"></div><div class="skeleton skeleton-card"></div></div>`;
   try {