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/globals.css

@@ -3335,6 +3335,12 @@ body:has([data-admin-viewport]) {
   padding-top: 0;
 }
 
+/* 用户积分表头吸顶：同 admin-users-stick，画布顶内边距必须归零 sticky 才能贴紧顶栏
+   （内边距挪到 .admin-points-users-tab；标记类仅在用户积分标签激活时挂载，不影响其他标签） */
+.admin-canvas:has(.admin-points-users-tab) {
+  padding-top: 0;
+}
+
 /* 移动端导航抽屉 */
 .admin-drawer {
   position: fixed;
@@ -5692,6 +5698,21 @@ a.j13-mention-token:hover {
     box-shadow: var(--shadow-sm);
   }
 
+  /* 用户积分标签：画布顶内边距挪到这里（见未分层区 canvas:has 规则），吸顶 th 才能贴齐 admin-topbar */
+  .admin-points-users-tab {
+    padding-top: 1.25rem;
+  }
+  @media (min-width: 640px) {
+    .admin-points-users-tab {
+      padding-top: 1.5rem;
+    }
+  }
+  @media (min-width: 1024px) {
+    .admin-points-users-tab {
+      padding-top: 1.75rem;
+    }
+  }
+
   /* 内容管理页：窄屏可整页滚；桌面高度由上方未分层的 canvas:has 规则锁定 */
   .admin-content-page {
     display: flex;
@@ -8409,6 +8430,78 @@ button.cmt-edited {
   text-decoration: underline;
   text-underline-offset: 2px;
 }
+/* 评论编辑历史：git diff 风格修订视图 */
+.cmt-diff {
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+}
+.cmt-diff-stat {
+  display: flex;
+  gap: 8px;
+  font-size: 11.5px;
+  font-weight: 600;
+  line-height: 1;
+  font-variant-numeric: tabular-nums;
+}
+.cmt-diff-stat-add {
+  color: var(--ok);
+}
+.cmt-diff-stat-del {
+  color: var(--danger);
+}
+.cmt-diff-body {
+  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, "Liberation Mono", monospace;
+  font-size: 12.5px;
+  line-height: 1.55;
+  background: var(--panel);
+  border: 1px solid var(--line);
+  border-radius: 6px;
+  padding: 4px 0;
+}
+.cmt-diff-line {
+  display: flex;
+  gap: 8px;
+  padding: 0 10px;
+  white-space: pre-wrap;
+  word-break: break-word;
+  min-height: 1.55em;
+}
+.cmt-diff-sign {
+  flex-shrink: 0;
+  width: 1ch;
+  user-select: none;
+  opacity: 0.65;
+}
+.cmt-diff-text {
+  min-width: 0;
+  flex: 1;
+}
+.cmt-diff-line.is-del {
+  background: color-mix(in srgb, var(--danger-soft) 60%, transparent);
+}
+.cmt-diff-line.is-add {
+  background: color-mix(in srgb, var(--ok-soft) 60%, transparent);
+}
+.cmt-diff-line.is-ctx {
+  color: var(--ink-2);
+}
+.cmt-diff-chg {
+  border-radius: 3px;
+  padding: 0 1px;
+  background: color-mix(in srgb, var(--danger) 24%, transparent);
+  color: inherit;
+}
+.cmt-diff-line.is-add .cmt-diff-chg {
+  background: color-mix(in srgb, var(--ok) 24%, transparent);
+}
+.cmt-diff-fold {
+  padding: 2px 10px;
+  font-size: 11.5px;
+  text-align: center;
+  color: var(--ink-2);
+  background: color-mix(in srgb, var(--ink) 3%, transparent);
+}
 .cmt-badge {
   display: inline-flex;
   align-items: center;