fix: add Docker socket mount and DOCKER_HOST to SaaS service

The cameleer-saas service needs Docker socket access for tenant
provisioning. Add the socket bind mount, group_add for permissions,
and explicit DOCKER_HOST=unix:///var/run/docker.sock to prevent
the Java Docker client from falling back to TCP (which happens on
WSL2 + Docker Desktop when DOCKER_HOST leaks from the host env).

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

installer/install.sh

@@ -840,6 +840,7 @@ EOF
       logto:
         condition: service_healthy
     environment:
+      DOCKER_HOST: unix:///var/run/docker.sock
       SPRING_DATASOURCE_URL: jdbc:postgresql://postgres:5432/cameleer_saas
       SPRING_DATASOURCE_USERNAME: ${POSTGRES_USER:-cameleer}
       SPRING_DATASOURCE_PASSWORD: ${POSTGRES_PASSWORD}