feat: 全站评论开关，并统一后台表单控件

关闭评论后前台隐藏评论能力；外观/设置/公告改用 AdminField 与 Stepper。

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

frontend/components/admin/AdminSearchField.tsx

@@ -3,7 +3,7 @@
 import { Search, X } from "lucide-react";
 import type { FormEvent } from "react";
 
-/** 左图标、可清除、Enter 提交；不要再并排「搜索」按钮 */
+/** 左图标、可清除、Enter 提交；壳层聚焦与聊天搜索一致 */
 export default function AdminSearchField({
   value,
   onChange,
@@ -30,11 +30,11 @@ export default function AdminSearchField({
   };
 
   return (
-    <form onSubmit={handleSubmit} className="relative flex-1 min-w-0" role="search">
+    <form onSubmit={handleSubmit} className="admin-field-shell admin-search-shell relative flex-1 min-w-0" role="search">
       <Search
         size={15}
-        className="absolute left-3.5 top-1/2 -translate-y-1/2 pointer-events-none"
-        style={{ color: "var(--ink-3)" }}
+        className="shrink-0 pointer-events-none"
+        style={{ color: value ? "var(--accent)" : "var(--ink-3)" }}
         aria-hidden
       />
       <input
@@ -43,14 +43,14 @@ export default function AdminSearchField({
         onChange={(e) => onChange(e.target.value)}
         placeholder={placeholder}
         aria-label={ariaLabel}
-        className="field pl-10 pr-9 py-2.5"
+        className="admin-field-input"
       />
       {value ? (
         <button
           type="button"
           onClick={clear}
           aria-label="清除搜索"
-          className="absolute right-2.5 top-1/2 -translate-y-1/2 w-6 h-6 inline-flex items-center justify-center rounded-full transition-colors hover:bg-[var(--panel-2)]"
+          className="w-6 h-6 inline-flex items-center justify-center rounded-full shrink-0 transition-colors hover:bg-[var(--accent-soft)]"
           style={{ color: "var(--ink-3)" }}
         >
           <X size={14} />