feat: implement QR code scan login system with admin control

- Add scan login service with Redis-based token management
- Add scan login API routes for token generation and validation
- Add QRCodeLogin component for PC-side QR code display
- Add EntryQRCode component for mass login scenarios
- Add ScanLoginView for mobile-side login form
- Add localStorage persistence for user identity
- Add logout functionality to mobile client
- Add auto-redirect for logged-in users
- Add admin console control for QR code display on big screen
- Add socket event forwarding from admin to screen display

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/client-mobile/src/views/HomeView.vue

@@ -1,5 +1,5 @@
 <script setup lang="ts">
-import { ref } from 'vue';
+import { ref, onMounted } from 'vue';
 import { useRouter } from 'vue-router';
 import { useConnectionStore } from '../stores/connection';
 import { showToast } from 'vant';
@@ -11,6 +11,14 @@ const userName = ref('');
 const userDept = ref('技术部');
 const isLoading = ref(false);
 
+// Check if already logged in
+onMounted(() => {
+  if (connectionStore.userId && connectionStore.userName && connectionStore.userName !== '访客') {
+    // Already logged in, redirect to vote page
+    router.replace('/vote');
+  }
+});
+
 async function handleEnter() {
   if (!userName.value.trim()) {
     showToast('请输入您的姓名');