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/app/admin/announcements/AnnouncementAdmin.tsx

@@ -25,6 +25,7 @@ import { toast } from "@/lib/toast";
 import ConfirmDialog from "@/components/ConfirmDialog";
 import {
   AdminEmpty,
+  AdminField,
   AdminIconButton,
   AdminPageHeader,
   AdminSegmented,
@@ -155,29 +156,24 @@ export default function AnnouncementAdmin({
               {form.id == null ? "新建公告" : "编辑公告"}
             </p>
 
-            <label className="field-label" htmlFor="anno-title">
-              标题
-            </label>
-            <input
+            <AdminField
               id="anno-title"
-              className="field mb-4"
+              className="mb-4"
+              label="标题"
               maxLength={200}
               value={form.title}
-              onChange={(e) => setForm({ ...form, title: e.target.value })}
+              onChange={(title) => setForm({ ...form, title })}
               placeholder="请输入公告标题"
             />
 
             <div className="flex items-end gap-4 mb-4 flex-wrap">
               <div className="w-36">
-                <label className="field-label" htmlFor="anno-tag">
-                  标签
-                </label>
-                <input
+                <AdminField
                   id="anno-tag"
-                  className="field"
+                  label="标签"
                   maxLength={32}
                   value={form.tag}
-                  onChange={(e) => setForm({ ...form, tag: e.target.value })}
+                  onChange={(tag) => setForm({ ...form, tag })}
                   placeholder="公告"
                 />
               </div>
@@ -213,14 +209,13 @@ export default function AnnouncementAdmin({
               />
             </div>
 
-            <label className="field-label" htmlFor="anno-content">
-              正文（支持 Markdown）
-            </label>
-            <textarea
+            <AdminField
               id="anno-content"
-              className="field min-h-[260px]"
+              label="正文（支持 Markdown）"
+              as="textarea"
+              minHeight="260px"
               value={form.content}
-              onChange={(e) => setForm({ ...form, content: e.target.value })}
+              onChange={(content) => setForm({ ...form, content })}
               placeholder="请输入公告正文，支持 Markdown 语法…"
             />