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/admin/settings/AccessSettings.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { ExternalLink, LogIn, MessageSquare, MessagesSquare, ShieldCheck, ShieldOff, Timer } from "lucide-react";
+import { ExternalLink, LogIn, MessageSquare, MessagesSquare, ShieldCheck, ShieldOff, Timer, Lock, Hourglass, Coins, History } from "lucide-react";
 import { useState } from "react";
 import {
   AdminSettingsGroup,
@@ -18,6 +18,59 @@ function InstantNote({ saving }: { saving?: boolean }) {
   return <span className="admin-settings-instant">{saving ? "正在保存…" : "修改后立即生效"}</span>;
 }
 
+/** 内容锁定 4 键（小时上限 8760 / 积分上限 100，后端裁剪） */
+type LockKeys = Pick<
+  PublicSettings,
+  "post_edit_lock_hours" | "comment_edit_lock_hours" | "necro_reply_after_hours" | "necro_reply_penalty"
+>;
+type LockKey = keyof LockKeys;
+
+const LOCK_META: { key: LockKey; icon: React.ReactNode; label: string; hint: string; max: number; unit: string; toast: (v: number) => string }[] = [
+  {
+    key: "post_edit_lock_hours",
+    icon: <Lock size={15} />,
+    label: "帖子可编辑时长",
+    hint: "发帖后仅在该时长内可编辑（0=不限制，上限 8760 小时），到期后编辑入口隐藏；管理团队不受限。",
+    max: 8760,
+    unit: "小时",
+    toast: (v) => (v === 0 ? "已关闭帖子编辑时限" : `帖子可编辑时长已设为 ${v} 小时`),
+  },
+  {
+    key: "comment_edit_lock_hours",
+    icon: <Hourglass size={15} />,
+    label: "评论可编辑时长",
+    hint: "评论发布后仅在该时长内可编辑（0=不限制，上限 8760 小时）；管理团队不受限。",
+    max: 8760,
+    unit: "小时",
+    toast: (v) => (v === 0 ? "已关闭评论编辑时限" : `评论可编辑时长已设为 ${v} 小时`),
+  },
+  {
+    key: "necro_reply_after_hours",
+    icon: <History size={15} />,
+    label: "旧帖回复判定时长",
+    hint: "回复超过该时长的帖子将提醒作者并按下方分值扣分（0=关闭，上限 8760 小时）；管理团队不受限。",
+    max: 8760,
+    unit: "小时",
+    toast: (v) => (v === 0 ? "已关闭旧帖回复提醒" : `旧帖判定时长已设为 ${v} 小时`),
+  },
+  {
+    key: "necro_reply_penalty",
+    icon: <Coins size={15} />,
+    label: "旧帖回复扣除积分",
+    hint: "触发旧帖回复时扣除的积分（0=仅提醒不扣分，上限 100）；积分不足将无法回复。",
+    max: 100,
+    unit: "分",
+    toast: (v) => (v === 0 ? "旧帖回复仅提醒不扣分" : `旧帖回复将扣除 ${v} 积分`),
+  },
+];
+
+const pickLock = (s: PublicSettings): LockKeys => ({
+  post_edit_lock_hours: s.post_edit_lock_hours,
+  comment_edit_lock_hours: s.comment_edit_lock_hours,
+  necro_reply_after_hours: s.necro_reply_after_hours,
+  necro_reply_penalty: s.necro_reply_penalty,
+});
+
 /** 内容互动开关 + 访问安全模块 */
 export default function AccessSettings({ initial }: { initial: PublicSettings }) {
   const [allowComments, setAllowComments] = useState(initial.allow_comments !== false);
@@ -37,8 +90,12 @@ export default function AccessSettings({ initial }: { initial: PublicSettings })
   const [togglingTrust, setTogglingTrust] = useState(false);
   const [togglingWithoutReview, setTogglingWithoutReview] = useState(false);
   const [savingCooldown, setSavingCooldown] = useState(false);
+  const [lockForm, setLockForm] = useState<LockKeys>(() => pickLock(initial));
+  const [savedLock, setSavedLock] = useState<LockKeys>(() => pickLock(initial));
+  const [savingLockKey, setSavingLockKey] = useState<LockKey | null>(null);
   const [moduleDirty, setModuleDirty] = useState(false);
-  const leave = useUnsavedGuard(moduleDirty);
+  const lockDirty = (Object.keys(savedLock) as LockKey[]).some((k) => lockForm[k] !== savedLock[k]);
+  const leave = useUnsavedGuard(moduleDirty || lockDirty);
 
   const toggleComments = async () => {
     if (togglingComments) return;
@@ -164,6 +221,23 @@ export default function AccessSettings({ initial }: { initial: PublicSettings })
     }
   };
 
+  const saveLock = async (key: LockKey) => {
+    if (savingLockKey) return;
+    const n = Math.max(0, Math.min(8760, Math.round(Number(lockForm[key])) || 0));
+    setSavingLockKey(key);
+    try {
+      const res = await apiUpdateSiteSettings({ [key]: n });
+      const saved = pickLock(res);
+      setLockForm((f) => ({ ...f, [key]: saved[key] }));
+      setSavedLock((f) => ({ ...f, [key]: saved[key] }));
+      toast(LOCK_META.find((m) => m.key === key)?.toast(saved[key]) || "已保存", "ok");
+    } catch (e) {
+      toast(e instanceof Error ? e.message : "保存失败");
+    } finally {
+      setSavingLockKey(null);
+    }
+  };
+
   return (
     <div className="admin-settings-stack">
       <AdminSettingsGroup title="内容与互动">
@@ -308,6 +382,31 @@ export default function AccessSettings({ initial }: { initial: PublicSettings })
           </div>
         </AdminSettingsRow>
       </AdminSettingsGroup>
+      <AdminSettingsGroup title="内容锁定与旧帖回复">
+        {LOCK_META.map((m) => (
+          <AdminSettingsRow key={m.key} label={<span className="inline-flex items-center gap-1.5">{m.icon} {m.label}</span>} hintBelow={m.hint}>
+            <div className="flex items-center gap-2 flex-wrap">
+              <AdminStepper
+                value={lockForm[m.key]}
+                onChange={(v) => setLockForm((f) => ({ ...f, [m.key]: v }))}
+                min={0}
+                max={m.max}
+                unit={m.unit}
+                ariaLabel={`${m.label}${m.unit}`}
+                disabled={savingLockKey !== null}
+              />
+              <button
+                type="button"
+                className="btn btn-line btn-sm"
+                disabled={savingLockKey !== null || lockForm[m.key] === savedLock[m.key]}
+                onClick={() => void saveLock(m.key)}
+              >
+                {savingLockKey === m.key ? "保存中…" : "保存"}
+              </button>
+            </div>
+          </AdminSettingsRow>
+        ))}
+      </AdminSettingsGroup>
       <OperationsPanel name="security" onDirtyChange={setModuleDirty} />
       <ConfirmDialog
         open={leave.leaveOpen}