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).

docker-compose.traefik.yml

@@ -23,4 +23,5 @@ services:
 
 networks:
   traefik:
+    name: ${TRAEFIK_NETWORK:-traefik}
     external: true