fix(bootstrap): detect docker desktop socket fallback on macos

[areporeporepo]

summary

this lets openshell detect docker desktop on macos when the daemon is reachable through ~/Library/Containers/com.docker.docker/Data/docker-cli.sock instead of /var/run/docker.sock.

changes

• probe the docker desktop macos socket alongside the existing colima and orbstack fallbacks
• retry alternative sockets before surfacing a docker preflight error when DOCKER_HOST is unset
• add unit coverage for the docker desktop socket path

testing

• cargo fmt --check
• cargo build -p openshell-bootstrap
• cargo test -p openshell-bootstrap

checklist

• follows conventional commits
• commits are signed off