chore: remove redundant DOCKER_HOST env var from SaaS service

TenantProvisionerAutoConfig already hardcodes the socket path via
.withDockerHost("unix:///var/run/docker.sock"). The env var was
redundant and not read by the Java Docker client.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -121,8 +121,6 @@ services:
       - certs:/certs
       - /var/run/docker.sock:/var/run/docker.sock
     environment:
-      # Docker
-      DOCKER_HOST: unix:///var/run/docker.sock
       # SaaS database
       SPRING_DATASOURCE_URL: jdbc:postgresql://postgres:5432/${POSTGRES_DB:-cameleer_saas}
       SPRING_DATASOURCE_USERNAME: ${POSTGRES_USER:-cameleer}