feat(desktop-client): 阶段4-6 Electron EXE 客户端（登录/课表/作业/通知/成绩/设置 + Socket.IO 实时 + IndexedDB 离线缓存与自动同步 + electron-builder 打包）

packages/desktop-client/src/renderer/App.vue

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+<script setup lang="ts">
+import { onMounted, ref } from 'vue';
+import { useRouter } from 'vue-router';
+import { useAppStore } from './stores/app.js';
+import { useAuthStore } from './stores/auth.js';
+import { useRealtimeStore } from './stores/realtime.js';
+
+const router = useRouter();
+const appStore = useAppStore();
+const auth = useAuthStore();
+const realtime = useRealtimeStore();
+
+const booting = ref(true);
+const bootText = ref('正在读取本地配置...');
+
+/**
+ * 启动流程：
+ * 1) 从主进程配置恢复服务器地址与登录令牌
+ * 2) 先用缓存资料渲染，再尝试向服务器刷新（不可达则进入离线会话）
+ * 3) 已登录则建立 Socket.IO 连接并进入主界面
+ */
+onMounted(async () => {
+  try {
+    bootText.value = '正在恢复登录状态...';
+    const session = await auth.restore();
+
+    // 连通性探测与健康轮询放到后台，不阻塞进入界面（离线时也能立刻看到缓存数据）
+    void appStore.init(session.serverUrl);
+
+    if (auth.token) realtime.connect(appStore.serverUrl, auth.token);
+
+    if (auth.isAuthenticated) await router.replace('/schedule');
+    else await router.replace('/login');
+  } finally {
+    booting.value = false;
+  }
+});
+</script>
+
+<template>
+  <div v-if="booting" class="boot-screen">
+    <el-icon :size="30" class="is-loading" color="#409eff"><Loading /></el-icon>
+    <p class="boot-title">班级小助手</p>
+    <p class="boot-text">{{ bootText }}</p>
+  </div>
+  <router-view v-else />
+</template>
+
+<style scoped>
+.boot-screen {
+  height: 100vh;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  gap: 10px;
+  background: linear-gradient(135deg, #1f2d3d 0%, #3a5169 60%, #409eff 100%);
+  color: #fff;
+}
+
+.boot-title {
+  margin: 6px 0 0;
+  font-size: 20px;
+  font-weight: 600;
+}
+
+.boot-text {
+  margin: 0;
+  font-size: 13px;
+  color: rgba(255, 255, 255, 0.75);
+}
+</style>