Implement Django backend and Vue frontend structure

- Django backend with projects, templates, exports apps
- SQLite database models for Project, Asset, CardLayer
- REST API endpoints for project management
- Vue frontend with Vite, Element Plus, Fabric.js
- Home page for project selection
- Editor page with Fabric.js canvas integration

frontend/src/App.vue

@@ -0,0 +1,23 @@
+<template>
+  <div id="app">
+    <router-view />
+  </div>
+</template>
+
+<script setup>
+</script>
+
+<style>
+* {
+  margin: 0;
+  padding: 0;
+  box-sizing: border-box;
+}
+
+#app {
+  font-family: 'Microsoft YaHei', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
+  -webkit-font-smoothing: antialiased;
+  -moz-osx-font-smoothing: grayscale;
+  color: #2c3e50;
+}
+</style>