feat(hide): 密码可见隐藏块，发帖双栏预览与门禁体验修复

增加密码解锁与游客签名 cookie；发帖页对齐 1440 并默认双栏预览；修复 locked 解析、按钮对比度与回复聚焦。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/components/CommentSection.tsx

@@ -136,6 +136,22 @@ export default function CommentSection({
     }
   }, [commentsOpen]);
 
+  // 登录回跳 / 隐藏块「去回复」：滚到评论框并聚焦
+  useEffect(() => {
+    if (!user || !commentsOpen) return;
+    const focusComposer = () => {
+      const hash = window.location.hash;
+      if (hash !== "#comment-input" && hash !== "#comments") return;
+      const el = textareaRef.current ?? document.getElementById("comment-input");
+      if (!(el instanceof HTMLTextAreaElement)) return;
+      el.scrollIntoView({ behavior: "smooth", block: "center" });
+      window.setTimeout(() => el.focus({ preventScroll: true }), 280);
+    };
+    focusComposer();
+    window.addEventListener("hashchange", focusComposer);
+    return () => window.removeEventListener("hashchange", focusComposer);
+  }, [user, commentsOpen]);
+
   const handleSubmit = async (e: React.FormEvent) => {
     e.preventDefault();
     if (!commentsOpen || !content.trim()) return;
@@ -1034,7 +1050,7 @@ export default function CommentSection({
   }
 
   return (
-    <section className="panel p-6 sm:p-8 mt-6" aria-label="评论区">
+    <section id="comments" className="panel p-6 sm:p-8 mt-6 scroll-mt-24" aria-label="评论区">
       <div className="flex items-center gap-2.5 mb-6">
         <h2 className="text-lg font-semibold" style={{ color: "var(--ink)" }}>
           评论
@@ -1063,7 +1079,7 @@ export default function CommentSection({
             }}
             placeholder="友善发言，发表一个新楼层..."
             rows={3}
-            className="field"
+            className="field scroll-mt-28"
             aria-label="写评论"
           />
           <div className="flex items-center justify-between gap-3 mt-2.5">