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/components/PostActions.tsx

@@ -3,9 +3,9 @@
 import { useState, useEffect, useRef } from "react";
 import { useRouter } from "next/navigation";
 import Link from "next/link";
-import { Pencil, Trash2, Pin, Star, SlidersHorizontal, ChevronDown, Check, BadgeCheck } from "lucide-react";
-import { apiMe, apiDeletePost, apiTogglePin, apiToggleRecommend, apiAdminApprovePost, type User } from "@/lib/api";
-import { canStaffSoftDelete, canModerateBoard, isAdminOrAbove } from "@/lib/roles";
+import { Pencil, Trash2, Pin, Star, SlidersHorizontal, ChevronDown, Check, BadgeCheck, Lock, LockOpen } from "lucide-react";
+import { apiMe, apiDeletePost, apiTogglePin, apiToggleRecommend, apiTogglePostLock, apiAdminApprovePost, type User } from "@/lib/api";
+import { canStaffSoftDelete, canModerateBoard, isAdminOrAbove, isStaff } from "@/lib/roles";
 import { toast } from "@/lib/toast";
 import ConfirmDialog from "@/components/ConfirmDialog";
 import StaffDeletePostModal from "@/components/StaffDeletePostModal";
@@ -19,6 +19,12 @@ interface PostActionsProps {
   recommended: boolean;
   /** 帖子审核状态：pending 时对可审者显示「通过评审」 */
   status: string;
+  /** 帖子创建时间：自动编辑锁计时基准（staff 豁免） */
+  createdAt: string;
+  /** 帖子是否被管理员手动锁定（staff 豁免） */
+  locked: boolean;
+  /** 帖子可编辑时长（小时）；0=不锁定；staff 豁免 */
+  postEditLockHours: number;
   /** 供删除确认展示 */
   title?: string;
 }
@@ -31,6 +37,9 @@ export default function PostActions({
   pinned,
   recommended,
   status,
+  createdAt,
+  locked,
+  postEditLockHours,
   title,
 }: PostActionsProps) {
   const router = useRouter();
@@ -39,6 +48,7 @@ export default function PostActions({
   const [deleting, setDeleting] = useState(false);
   const [isPinned, setIsPinned] = useState(pinned > 0);
   const [isRecommended, setIsRecommended] = useState(recommended);
+  const [isLocked, setIsLocked] = useState(locked);
   const [acting, setActing] = useState(false);
   const [confirmDelete, setConfirmDelete] = useState(false);
   const [staffDeleteOpen, setStaffDeleteOpen] = useState(false);
@@ -70,6 +80,13 @@ export default function PostActions({
     !!user &&
     (user.id === authorId || canStaffSoftDelete(user, boardId, authorRole));
   const isAdmin = !!user && isAdminOrAbove(user.role);
+  const staffUser = !!user && isStaff(user.role);
+  // 编辑入口：手动锁帖或超过可编辑时限时对普通用户隐藏，staff 豁免
+  const editTimeLocked =
+    !staffUser &&
+    postEditLockHours > 0 &&
+    Date.now() - new Date(createdAt).getTime() > postEditLockHours * 3_600_000;
+  const showEdit = canManage && !(isLocked && !staffUser) && !editTimeLocked;
   const canApprove =
     !!user && status === "pending" && canModerateBoard(user, boardId);
   // staff 删他人帖：走类型+理由；作者自删：简单确认
@@ -139,6 +156,21 @@ export default function PostActions({
     }
   };
 
+  const handleLock = async () => {
+    setActing(true);
+    setOpen(false);
+    try {
+      const res = await apiTogglePostLock(postId);
+      setIsLocked(res.locked);
+      toast(res.locked ? "已锁定，普通用户不可编辑与回复" : "已解除锁定", "ok");
+      router.refresh();
+    } catch {
+      toast("操作失败，请稍后重试");
+    } finally {
+      setActing(false);
+    }
+  };
+
   if (!canManage) return null;
 
   const itemCls =
@@ -212,18 +244,35 @@ export default function PostActions({
                 <span className="flex-1 text-left">{isRecommended ? "取消推荐" : "推荐"}</span>
                 {isRecommended && <Check size={14} className="shrink-0" />}
               </button>
+              <button
+                type="button"
+                role="menuitem"
+                onClick={handleLock}
+                className={itemCls}
+                style={isLocked ? { color: "var(--danger)" } : { color: "var(--ink)" }}
+              >
+                {isLocked ? (
+                  <LockOpen size={14} className="shrink-0" />
+                ) : (
+                  <Lock size={14} className="shrink-0" />
+                )}
+                <span className="flex-1 text-left">{isLocked ? "解除锁定" : "锁定"}</span>
+                {isLocked && <Check size={14} className="shrink-0" />}
+              </button>
               <div style={{ height: 1, background: "var(--line)" }} />
             </>
           )}
-          <Link
-            href={`/post/${postId}/edit`}
-            role="menuitem"
-            className={`${itemCls} items-center`}
-            style={{ color: "var(--ink)" }}
-          >
-            <Pencil size={14} className="shrink-0" />
-            <span className="flex-1 text-left">编辑帖子</span>
-          </Link>
+          {showEdit && (
+            <Link
+              href={`/post/${postId}/edit`}
+              role="menuitem"
+              className={`${itemCls} items-center`}
+              style={{ color: "var(--ink)" }}
+            >
+              <Pencil size={14} className="shrink-0" />
+              <span className="flex-1 text-left">编辑帖子</span>
+            </Link>
+          )}
           <button
             type="button"
             role="menuitem"