RestaurantPOS App Stack (skeleton)

Placeholder for a future app using shared modules from ../../modules.

• Env/region stacks will live under envs/<env>/<region>/ (backend.tf + *.tfvars + main.tf).
• App composition will live under app_stack/ (ECS services, ALB, DB/cache/S3 as needed).
• Images will come from the RestaurantPOS app Dockerfiles and be referenced in tfvars.