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/apps/exports/urls.py

@@ -0,0 +1,7 @@
+from django.urls import path
+from .views import export_project, export_single_card
+
+urlpatterns = [
+    path('projects/<str:pk>/export/', export_project, name='export-project'),
+    path('projects/<str:pk>/export/<str:card_key>/', export_single_card, name='export-single-card'),
+]