fix: frontend and backend now get variables at build time not runtime

.github/workflows/deploy.yml

@@ -39,6 +39,8 @@ jobs:
           context: ./frontend
           push: true
           tags: ${{ secrets.DOCKERHUB_USERNAME }}/werkzeugkiste-frontend:latest
+          build-args: |
+            NEXT_PUBLIC_BACKEND_URL=${{ secrets.NEXT_PUBLIC_BACKEND_URL }}
 
       - name: Build and Push Backend
         uses: docker/build-push-action@v6
@@ -46,6 +48,8 @@ jobs:
           context: ./backend
           push: true
           tags: ${{ secrets.DOCKERHUB_USERNAME }}/werkzeugkiste-backend:latest
+          build-args: |
+              CORS_ALLOWED_ORIGIN=${{ secrets.CORS_ALLOWED_ORIGIN }}
 
   deploy-on-server:
     needs: docker-build-push