fix: redirect to login page when user tries to register lottery without login

frontend/src/views/user/LotteryDetail.vue

@@ -21,12 +21,13 @@
 
 <script setup lang="ts">
 import { ref, onMounted } from 'vue'
-import { useRoute } from 'vue-router'
+import { useRoute, useRouter } from 'vue-router'
 import { ElMessage } from 'element-plus'
 import { lotteryApi } from '../../api'
 import BackNav from '../../components/BackNav.vue'
 
 const route = useRoute()
+const router = useRouter()
 const lottery = ref<any>(null)
 
 const prizeTypeMap: Record<string, string> = {
@@ -59,6 +60,7 @@ async function register() {
   const token = localStorage.getItem('token')
   if (!token) {
     ElMessage.warning('请先登录后再报名')
+    router.push('/login')
     return
   }