feat(系统设置): 新增系统设置模块

- 添加SystemSetting模型用于存储系统配置
- 实现系统设置API路由，支持CRUD操作
- 新增系统设置前端页面，包含全局配置、外观设置、数据备份和关于页面
- 设备批量操作增强，支持批量移动、状态变更和导出
- 工单模型允许deviceId为空

frontend/src/App.jsx

@@ -1,6 +1,6 @@
 import React, { useState, Suspense, lazy } from 'react';
 import { Layout, Menu, theme, Button, Dropdown, Avatar, message, Space, Divider } from 'antd';
-import { BarChartOutlined, DatabaseOutlined, CloudServerOutlined, MenuUnfoldOutlined, MenuFoldOutlined, EyeOutlined, BuildOutlined, HomeOutlined, ShoppingCartOutlined, InboxOutlined, ImportOutlined, FileTextOutlined, UserOutlined, LogoutOutlined, HistoryOutlined, AuditOutlined, ToolOutlined, ScheduleOutlined } from '@ant-design/icons';
+import { BarChartOutlined, DatabaseOutlined, CloudServerOutlined, MenuUnfoldOutlined, MenuFoldOutlined, EyeOutlined, BuildOutlined, HomeOutlined, ShoppingCartOutlined, InboxOutlined, ImportOutlined, FileTextOutlined, UserOutlined, LogoutOutlined, HistoryOutlined, AuditOutlined, ToolOutlined, ScheduleOutlined, SettingOutlined } from '@ant-design/icons';
 import { BrowserRouter as Router, Routes, Route, Link, Navigate, useLocation, useNavigate } from 'react-router-dom';
 import { useAuth } from './context/AuthContext';
 import { Spin } from 'antd';
@@ -23,6 +23,7 @@ const TicketManagement = lazy(() => import('./pages/TicketManagement'));
 const TicketCategoryManagement = lazy(() => import('./pages/TicketCategoryManagement'));
 const TicketStatistics = lazy(() => import('./pages/TicketStatistics'));
 const TicketFieldManagement = lazy(() => import('./pages/TicketFieldManagement'));
+const SystemSettings = lazy(() => import('./pages/SystemSettings'));
 
 const { Header, Content, Sider } = Layout;
 
@@ -226,6 +227,11 @@ const AppLayout = ({ children }) => {
                   icon: <AuditOutlined />,
                   label: <Link to="/operation-logs">操作日志</Link>,
                 },
+                {
+                  key: 'system-settings',
+                  icon: <SettingOutlined />,
+                  label: <Link to="/settings">系统设置</Link>,
+                },
               ],
             },
             {
@@ -463,6 +469,14 @@ function App() {
             </PrivateRoute>
           }
         />
+        <Route
+          path="/settings"
+          element={
+            <PrivateRoute>
+              <SystemSettings />
+            </PrivateRoute>
+          }
+        />
         <Route path="*" element={<Navigate to="/" replace />} />
       </Routes>
     </Router>