PRD 0007: stop tunneling ssh through pipelock. Each Host block in
the agent's ~/.ssh/config now points at the gate container + the
per-entry listen port; HostKeyAlias preserves host-key validation
against the real upstream name, and CheckHostIP=no skips the
resolved-IP path (which would otherwise hit the gate's IP).
known_hosts collapses to a single entry per upstream keyed on the
alias.
The pipelock_proxy_host_port import is gone from this module; the
function itself becomes dead code and gets removed alongside the
broader pipelock SSH carve-outs in the next commit.
didericis