feat: add AirShelf core implementation

core/backend/apps/assets/urls.py

@@ -0,0 +1,11 @@
+from django.urls import path
+from rest_framework.routers import DefaultRouter
+
+from .views import AssetUploadView, AssetViewSet
+
+router = DefaultRouter()
+router.register("", AssetViewSet, basename="asset")
+
+urlpatterns = [
+    path("upload/", AssetUploadView.as_view(), name="asset-upload"),
+] + router.urls