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/layout.tsx

@@ -11,6 +11,7 @@ import ThemeSync from "@/components/ThemeSync";
 import RealtimeProvider from "@/components/RealtimeProvider";
 import CodeFoldProvider from "@/components/markdown/CodeFoldProvider";
 import MotionProvider from "@/components/MotionProvider";
+import CommentsPolicyProvider from "@/components/CommentsPolicyProvider";
 import type { User } from "@/lib/api";
 import { getMeCached, getPublicSettingsCached } from "@/lib/serverData";
 import { TOKEN_COOKIE, authCookieHeader } from "@/lib/cookies";
@@ -126,12 +127,14 @@ export default async function RootLayout({
           className="flex-1 w-full max-w-[1440px] mx-auto px-4 sm:px-6 py-7 sm:py-9 outline-none"
         >
           <MotionProvider initial={motionCfg}>
-            <CodeFoldProvider
-              initialEnabled={settings.code_block_auto_fold}
-              initialFoldLines={settings.code_block_fold_lines}
-            >
-              {children}
-            </CodeFoldProvider>
+            <CommentsPolicyProvider allowComments={settings.allow_comments !== false}>
+              <CodeFoldProvider
+                initialEnabled={settings.code_block_auto_fold}
+                initialFoldLines={settings.code_block_fold_lines}
+              >
+                {children}
+              </CodeFoldProvider>
+            </CommentsPolicyProvider>
           </MotionProvider>
         </main>
         <Footer siteName={settings.site_name} />