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/home/FeedTabs.tsx

@@ -4,6 +4,7 @@ import Link from "next/link";
 import { useRouter } from "next/navigation";
 import { useRef } from "react";
 import { MessageSquareText, Clock, Sparkles } from "lucide-react";
+import { useAllowComments } from "@/components/CommentsPolicyProvider";
 
 export type FeedSort = "latest" | "new" | "recommended";
 
@@ -22,18 +23,20 @@ function tabHref(key: FeedSort, boardId: number) {
 export default function FeedTabs({ current, boardId = 0 }: { current: FeedSort; boardId?: number }) {
   const router = useRouter();
   const tabRefs = useRef<(HTMLAnchorElement | null)[]>([]);
+  const allowComments = useAllowComments();
+  const keys = allowComments ? TAB_KEYS : TAB_KEYS.filter((k) => k !== "latest");
 
   const handleKeyDown = (e: React.KeyboardEvent, i: number) => {
     if (e.key !== "ArrowRight" && e.key !== "ArrowLeft") return;
     e.preventDefault();
-    const next = (i + (e.key === "ArrowRight" ? 1 : TAB_KEYS.length - 1)) % TAB_KEYS.length;
+    const next = (i + (e.key === "ArrowRight" ? 1 : keys.length - 1)) % keys.length;
     tabRefs.current[next]?.focus();
-    router.push(tabHref(TAB_KEYS[next], boardId));
+    router.push(tabHref(keys[next], boardId));
   };
 
   return (
     <div className="flex items-center gap-1.5 sm:gap-2" role="tablist" aria-label="帖子排序">
-      {TAB_KEYS.map((key, i) => {
+      {keys.map((key, i) => {
         const Icon = key === "latest" ? MessageSquareText : key === "new" ? Clock : Sparkles;
         return (
           <Link