feat: initialize Gradle multi-module backend and Vite frontend

frontend/packages/app/src/App.vue

@@ -0,0 +1,47 @@
+<script setup lang="ts">
+const online = ref(true)
+</script>
+
+<template>
+  <main class="shell">
+    <header class="topbar">
+      <span class="status-dot" :class="{ offline: !online }" />
+      <h1>IM 聊天</h1>
+    </header>
+    <section class="content">
+      <p>前端骨架就绪（Vue 3 + TypeScript + Vite），可无缝迁移至 Tauri。</p>
+    </section>
+  </main>
+</template>
+
+<style scoped>
+.shell {
+  display: flex;
+  flex-direction: column;
+  height: 100vh;
+}
+
+.topbar {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  padding: 12px 16px;
+  border-bottom: 1px solid #e5e7eb;
+}
+
+.status-dot {
+  width: 8px;
+  height: 8px;
+  border-radius: 50%;
+  background: #22c55e;
+}
+
+.status-dot.offline {
+  background: #9ca3af;
+}
+
+.content {
+  flex: 1;
+  padding: 16px;
+}
+</style>

frontend/packages/app/src/main.ts

@@ -0,0 +1,8 @@
+import { createApp } from 'vue'
+import { createPinia } from 'pinia'
+import App from './App.vue'
+
+const app = createApp(App)
+
+app.use(createPinia())
+app.mount('#app')

frontend/packages/app/src/vite-env.d.ts

@@ -0,0 +1,7 @@
+/// <reference types="vite/client" />
+
+declare module '*.vue' {
+  import type { DefineComponent } from 'vue'
+  const component: DefineComponent<Record<string, never>, Record<string, never>, unknown>
+  export default component
+}