统一 React 管理后台，修复评论换行与帖子置顶

- /admin/* 全部由 React SPA 渲染，替代旧版 HTML 后台页面
- 新增仪表盘、帖子/评论/用户管理、系统设置与 JSON API
- 帖子详情页支持管理员置顶；评论换行显示修复

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/pages/admin/AdminUsersPage.tsx

@@ -0,0 +1,110 @@
+import { useEffect, useState } from 'react';
+import { Button } from '@/components/ui/button';
+import { Badge } from '@/components/ui/badge';
+import { Spinner } from '@/components/ui/spinner';
+import { notify } from '@/lib/notify';
+import { api } from '../../api/client';
+import { useAdminGuard } from '../../layouts/AdminLayout';
+import type { User } from '../../api/types';
+
+export default function AdminUsersPage() {
+  const { ready } = useAdminGuard();
+  const [users, setUsers] = useState<User[]>([]);
+  const [loading, setLoading] = useState(true);
+  const [page, setPage] = useState(1);
+  const [totalPages, setTotalPages] = useState(1);
+
+  const load = (p = page) => {
+    setLoading(true);
+    api.adminUsers(p)
+      .then(d => {
+        setUsers(d.users ?? []);
+        setPage(d.page);
+        setTotalPages(d.total_pages);
+      })
+      .catch(e => notify.error(e.message))
+      .finally(() => setLoading(false));
+  };
+
+  useEffect(() => {
+    if (ready) load(1);
+  }, [ready]);
+
+  const toggleBan = async (user: User) => {
+    if (user.role === 'admin') {
+      notify.warning('不能禁言管理员');
+      return;
+    }
+    try {
+      const r = await api.adminBanUser(user.id, !user.banned);
+      notify.success(r.message);
+      load();
+    } catch (e: unknown) {
+      notify.error(e instanceof Error ? e.message : '操作失败');
+    }
+  };
+
+  if (!ready) return null;
+
+  return (
+    <div className="admin-page">
+      <div className="admin-page-head">
+        <h1>用户管理</h1>
+        <p>查看注册用户，禁言或解除禁言</p>
+      </div>
+
+      <div className="admin-card">
+        {loading ? (
+          <div className="flex justify-center py-12"><Spinner size="lg" /></div>
+        ) : (
+          <>
+            <table className="admin-table">
+              <thead>
+                <tr>
+                  <th>ID</th>
+                  <th>用户名</th>
+                  <th>昵称</th>
+                  <th>角色</th>
+                  <th>状态</th>
+                  <th>注册时间</th>
+                  <th>操作</th>
+                </tr>
+              </thead>
+              <tbody>
+                {users.map(u => (
+                  <tr key={u.id}>
+                    <td>{u.id}</td>
+                    <td>{u.username}</td>
+                    <td>{u.nickname}</td>
+                    <td>
+                      {u.role === 'admin'
+                        ? <Badge variant="orange">管理员</Badge>
+                        : <Badge variant="secondary">用户</Badge>}
+                    </td>
+                    <td>{u.banned ? <Badge variant="destructive">已禁言</Badge> : '正常'}</td>
+                    <td>{u.created_at ? new Date(u.created_at).toLocaleString('zh-CN') : '—'}</td>
+                    <td>
+                      {u.role !== 'admin' && (
+                        <Button size="sm" variant="outline" onClick={() => toggleBan(u)}>
+                          {u.banned ? '解除禁言' : '禁言'}
+                        </Button>
+                      )}
+                    </td>
+                  </tr>
+                ))}
+              </tbody>
+            </table>
+            {users.length === 0 && <div className="admin-empty">暂无用户</div>}
+            {totalPages > 1 && (
+              <div className="admin-pagination">
+                <Button size="sm" variant="outline" disabled={page <= 1} onClick={() => load(page - 1)}>上一页</Button>
+                <span>第 {page} / {totalPages} 页</span>
+                <Button size="sm" variant="outline" disabled={page >= totalPages} onClick={() => load(page + 1)}>下一页</Button>
+              </div>
+            )}
+          </>
+        )}
+      </div>
+    </div>
+  );
+}