refactor(docker): replace env_file with explicit environment variables

- Remove env_file references from docker-compose.yml and docker-compose.prod.yml
- Add explicit environment variable forwarding for all services
- Use TRAEFIK_NETWORK env var in docker-compose.traefik.yml instead of hardcoded name
- Add VITE_* frontend variables to .env.example and deploy/.env.example
- Add missing production variables (TRAEFIK_ENTRYPOINT, TRAEFIK_CERT_RESOLVER) to deploy/.env.example

This makes environment configuration more explicit and easier to manage
across different deployment scenarios (local dev, CI/CD, Portainer).

deploy/.env.example

@@ -20,8 +20,16 @@ SECRET_ENCRYPTION_KEY=change-me-in-production
 ACCESS_TOKEN_EXPIRE_MINUTES=60
 
 # Deployment
+TRAEFIK_NETWORK=traefik
 TRAEFIK_LOG_LEVEL=INFO
+TRAEFIK_ENTRYPOINT=websecure
+TRAEFIK_CERT_RESOLVER=letsencrypt
 API_TAG=latest
 WEB_TAG=latest
 REGISTRY=ghcr.io
 REPO=headquarter
+
+# Frontend build-time variables
+VITE_API_URL=https://api.example.com
+VITE_OIDC_ISSUER=https://auth.example.com/application/o/headquarter/
+VITE_OIDC_CLIENT_ID=headquarter-web