fix: make traefik network configurable in docker-compose.traefik.yml

- Replace hardcoded 'traefik' network references with configurable
  traefik in both api and web services
- Network definition at bottom already supported configuration,
  but service references were still hardcoded

docker-compose.traefik.yml

@@ -73,7 +73,7 @@ services:
         condition: service_healthy
     networks:
       - backend
-      - traefik
+      - ${TRAEFIK_NETWORK:-traefik}
     restart: unless-stopped
     labels:
       - "traefik.enable=true"
@@ -97,7 +97,7 @@ services:
       - api
     networks:
       - backend
-      - traefik
+      - ${TRAEFIK_NETWORK:-traefik}
     restart: unless-stopped
     labels:
       - "traefik.enable=true"