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/app/compose/layout.tsx

@@ -10,7 +10,7 @@ export default function ComposeLayout({
   return (
     <div
       data-compose-viewport
-      className="flex flex-col flex-1 min-h-0 w-full max-w-6xl mx-auto"
+      className="flex flex-col flex-1 min-h-0 w-full"
     >
       {children}
     </div>