Fix frontend container app dir ownership for Vite

doc/operations-and-configuration.md

@@ -102,6 +102,10 @@ Selected defaults from `Settings` (`backend/app/core/config.py`):
 Frontend runtime API target:
 - `VITE_API_BASE` in `docker-compose.yml` frontend service
 
+Frontend container runtime behavior:
+- the container runs as non-root `node`
+- `/app` is owned by `node` in `frontend/Dockerfile` so Vite can create runtime temp config files under `/app`
+
 Frontend local commands:
 
 ```bash