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

backend/requirements.txt

@@ -0,0 +1,10 @@
+# Django核心
+Django>=5.0,<6.0
+djangorestframework>=3.14
+django-cors-headers>=4.3
+
+# 图像处理
+Pillow>=10.0
+
+# 其他工具
+python-dotenv>=1.0