feat: add guest login button for customer demos

- One-click "访客体验入口" button on login page
- Visitor account (visitor/visitor123) with read-only role
- No username/password needed for customers to browse

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/pages/Login/index.tsx

@@ -9,14 +9,20 @@ const { Title, Text } = Typography;
 
 export default function LoginPage() {
   const [loading, setLoading] = useState(false);
+  const [guestLoading, setGuestLoading] = useState(false);
   const navigate = useNavigate();
 
+  const doLogin = async (username: string, password: string) => {
+    const res: any = await login(username, password);
+    setToken(res.access_token);
+    setUser(res.user);
+    return res;
+  };
+
   const onFinish = async (values: { username: string; password: string }) => {
     setLoading(true);
     try {
-      const res: any = await login(values.username, values.password);
-      setToken(res.access_token);
-      setUser(res.user);
+      await doLogin(values.username, values.password);
       message.success('登录成功');
       navigate('/');
     } catch {
@@ -26,6 +32,19 @@ export default function LoginPage() {
     }
   };
 
+  const onGuestLogin = async () => {
+    setGuestLoading(true);
+    try {
+      await doLogin('visitor', 'visitor123');
+      message.success('访客登录成功');
+      navigate('/');
+    } catch {
+      message.error('访客登录失败，请联系管理员');
+    } finally {
+      setGuestLoading(false);
+    }
+  };
+
   return (
     <div style={{
       minHeight: '100vh', display: 'flex', justifyContent: 'center', alignItems: 'center',
@@ -51,9 +70,17 @@ export default function LoginPage() {
               登 录
             </Button>
           </Form.Item>
-          {import.meta.env.DEV && <Text type="secondary" style={{ fontSize: 12 }}>
-            默认账号: admin / admin123
-          </Text>}
+          <Form.Item style={{ marginBottom: 8 }}>
+            <Button block loading={guestLoading} onClick={onGuestLogin}
+              style={{ borderColor: '#1890ff', color: '#1890ff' }}>
+              访客体验入口
+            </Button>
+          </Form.Item>
+          <div style={{ textAlign: 'center' }}>
+            <Text type="secondary" style={{ fontSize: 12 }}>
+              访客仅可浏览数据，无管理权限
+            </Text>
+          </div>
         </Form>
       </Card>
     </div>

scripts/seed_data.py

@@ -108,6 +108,9 @@ async def seed():
             User(username="operator1", hashed_password=hash_password("tianpu123"),
                  full_name="李运维", role="operator", email="op1@tianpu.com",
                  phone="13800000003"),
+            User(username="visitor", hashed_password=hash_password("visitor123"),
+                 full_name="访客", role="visitor", email=None,
+                 phone=None),
         ]
         session.add_all(users)