The Docker socket group varies by host (e.g., GID 1001 on WSL2).
Hardcoding group_add: ["0"] doesn't work when the socket is owned
by a different group. The installer now detects the socket GID at
install time via stat. The main docker-compose.yml uses a
configurable DOCKER_GID env var (defaults to 0).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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