feat(web): add login page, auth store, API client, and route guard

- API client with axios interceptors: JWT attach + 401 auto-refresh
- Auth store (Zustand): login/logout/loadFromStorage with localStorage
- Login page: gradient background, Ant Design form, error handling
- Home page: dashboard with statistics cards
- App.tsx: PrivateRoute guard, /login route, auth state restoration
- MainLayout: dynamic user display, logout dropdown, menu navigation
- Users API service: CRUD with pagination support

apps/web/src/pages/Home.tsx

@@ -0,0 +1,37 @@
+import { Typography, Card, Row, Col, Statistic } from 'antd';
+import {
+  UserOutlined,
+  TeamOutlined,
+  FileTextOutlined,
+  BellOutlined,
+} from '@ant-design/icons';
+
+export default function Home() {
+  return (
+    <div>
+      <Typography.Title level={4}>工作台</Typography.Title>
+      <Row gutter={[16, 16]}>
+        <Col xs={24} sm={12} md={6}>
+          <Card>
+            <Statistic title="用户总数" value={0} prefix={<UserOutlined />} />
+          </Card>
+        </Col>
+        <Col xs={24} sm={12} md={6}>
+          <Card>
+            <Statistic title="角色数量" value={0} prefix={<TeamOutlined />} />
+          </Card>
+        </Col>
+        <Col xs={24} sm={12} md={6}>
+          <Card>
+            <Statistic title="流程实例" value={0} prefix={<FileTextOutlined />} />
+          </Card>
+        </Col>
+        <Col xs={24} sm={12} md={6}>
+          <Card>
+            <Statistic title="未读消息" value={0} prefix={<BellOutlined />} />
+          </Card>
+        </Col>
+      </Row>
+    </div>
+  );
+}