feat(auth): 添加登录功能和路由保护

- 在侧边栏添加退出登录按钮并实现登出逻辑
- 添加 ProtectedRoute 组件用于路由权限控制
- 创建 LoginPage 组件实现登录界面和逻辑
- 集成本地登录验证到 authSlice 状态管理
- 配置路由表添加登录页面和保护路由
- 实现自动跳转到登录页面的重定向逻辑

frontend/src/components/ProtectedRoute.tsx

@@ -0,0 +1,21 @@
+import React from 'react';
+import { Navigate, useLocation, Outlet } from 'react-router';
+import { useAppSelector } from '@/store/hooks';
+
+interface ProtectedRouteProps {
+  children?: React.ReactNode;
+}
+
+const ProtectedRoute: React.FC<ProtectedRouteProps> = ({ children }) => {
+  const { isAuthenticated } = useAppSelector((state) => state.auth);
+  const location = useLocation();
+
+  if (!isAuthenticated) {
+    // Redirect to the login page, but save the current location they were trying to go to
+    return <Navigate to="/login" state={{ from: location }} replace />;
+  }
+
+  return children ? <>{children}</> : <Outlet />;
+};
+
+export default ProtectedRoute;