fix(mining-admin-web): 修复用户列表页面空数据和错误处理

- 修复 data.items 可能为 undefined 导致的崩溃
- 添加 API 错误状态显示

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/mining-admin-web/src/app/(dashboard)/users/page.tsx

@@ -22,7 +22,7 @@ export default function UsersPage() {
   const [page, setPage] = useState(1);
   const pageSize = 20;
 
-  const { data, isLoading } = useUsers({ page, pageSize, keyword: searchKeyword });
+  const { data, isLoading, error } = useUsers({ page, pageSize, keyword: searchKeyword });
 
   const handleSearch = () => {
     setSearchKeyword(keyword);
@@ -102,14 +102,20 @@ export default function UsersPage() {
                       ))}
                     </TableRow>
                   ))
-                ) : data?.items.length === 0 ? (
+                ) : error ? (
+                  <TableRow>
+                    <TableCell colSpan={12} className="text-center py-8 text-red-500">
+                      加载失败: {(error as Error)?.message || '请稍后重试'}
+                    </TableCell>
+                  </TableRow>
+                ) : !data?.items || data.items.length === 0 ? (
                   <TableRow>
                     <TableCell colSpan={12} className="text-center py-8 text-muted-foreground">
                       暂无数据
                     </TableCell>
                   </TableRow>
                 ) : (
-                  data?.items.map((user) => (
+                  data.items.map((user) => (
                     <TableRow key={user.accountSequence}>
                       {/* 头像 */}
                       <TableCell>
@@ -195,7 +201,7 @@ export default function UsersPage() {
             </Table>
           </div>
 
-          {data && data.totalPages > 1 && (
+          {data?.items && data.totalPages > 1 && (
             <div className="flex items-center justify-between p-4 border-t">
               <p className="text-sm text-muted-foreground">
                 共 {formatNumber(data.total)} 条，第 {page} / {data.totalPages} 页