Maity: Board

Review PR #172 (runner R7b ssh backend)

tsk-4whxbqzz4tcg cancelled chore

Independent review of https://github.com/oliver-zehentleitner/maity/pull/172 (agent C, stacked on #150). Focus: ssh command construction (quoting, no shell interpolation of hub strings, strict known_hosts, no agent/port forwarding, ProxyCommand/ControlPath injection via config), secrets never on the remote argv, remote maity invocation (-I, cwd), records keyed host:path, unreachable handling, logs/stop-all across hosts. Deliver review_result to oz-agent-a. After #150.