feat: 评论/帖子编辑历史与编辑标记，内容锁定

- 新增 smartDiff 差异计算与 EditHistoryModal 编辑历史弹窗，替换原 CommentEditHistoryModal
- 新增 PostEditedMark 编辑标记展示
- 新增内容锁定机制（content_lock）防止并发编辑冲突
- 审核与通知服务适配

frontend/app/notifications/NotificationsClient.tsx

@@ -3,7 +3,7 @@
 import { useState } from "react";
 import { useRouter } from "next/navigation";
 import Link from "next/link";
-import { Heart, MessageCircle, CheckCheck, Bell, CheckCircle2, XCircle, AtSign, ClipboardList, Award } from "lucide-react";
+import { Heart, MessageCircle, CheckCheck, Bell, CheckCircle2, XCircle, AtSign, ClipboardList, Award, AlertTriangle } from "lucide-react";
 import { apiMarkRead, apiMarkAllRead, type NotificationsResponse, type NotificationItem } from "@/lib/api";
 
 /**
@@ -76,22 +76,26 @@ export default function NotificationsClient({ initialData }: { initialData: Noti
         <div className="panel overflow-hidden p-0">
           {notifications.map((n, i) => {
             const approval = n.type === "approved" || n.type === "rejected";
+            // 系统提醒（ActorID=0）：不渲染操作者链接，仅展示标题与内容
+            const system = n.type === "necro_reply";
             const iconNode = n.type === "approved"
               ? <CheckCircle2 size={16} />
               : n.type === "rejected" || n.type === "deleted"
                 ? <XCircle size={16} />
-                : n.type === "like"
-                  ? <Heart size={16} />
-                  : n.type === "mention"
-                    ? <AtSign size={16} />
-                    : n.type === "pending_review"
-                      ? <ClipboardList size={16} />
-                      : n.type === "badge"
-                        ? <Award size={16} />
-                        : <MessageCircle size={16} />;
+                : n.type === "necro_reply"
+                  ? <AlertTriangle size={16} />
+                  : n.type === "like"
+                    ? <Heart size={16} />
+                    : n.type === "mention"
+                      ? <AtSign size={16} />
+                      : n.type === "pending_review"
+                        ? <ClipboardList size={16} />
+                        : n.type === "badge"
+                          ? <Award size={16} />
+                          : <MessageCircle size={16} />;
             const iconColor = n.type === "approved"
               ? "var(--ok)"
-              : n.type === "rejected" || n.type === "deleted"
+              : n.type === "rejected" || n.type === "deleted" || n.type === "necro_reply"
                 ? "var(--danger)"
                 : n.type === "like"
                   ? "var(--clay)"
@@ -100,7 +104,7 @@ export default function NotificationsClient({ initialData }: { initialData: Noti
                     : "var(--accent)";
             const iconBg = n.type === "approved"
               ? "var(--ok-soft)"
-              : n.type === "rejected" || n.type === "deleted"
+              : n.type === "rejected" || n.type === "deleted" || n.type === "necro_reply"
                 ? "var(--danger-soft)"
                 : n.type === "like"
                   ? "var(--clay-soft)"
@@ -133,6 +137,10 @@ export default function NotificationsClient({ initialData }: { initialData: Noti
                     >
                       {n.type === "approved" ? "审核通过" : "未通过审核"}
                     </span>
+                  ) : system ? (
+                    <span className="font-bold" style={{ color: "var(--danger)" }}>
+                      旧帖回复提醒
+                    </span>
                   ) : (
                     <>
                       <Link