[codex] fix: wait for SSH listener IP at startup

[wk1995]

Summary

• Make address-bound SSH wait for network readiness and the configured listener IP before starting.
• Preserve the fixed private-address listener and existing SSH hardening.
• Record the internal operational change without modifying published B-side protocol documents.

Root cause

On reboot, sshd could run before the gateway's static listener address was assigned, causing Cannot assign requested address and leaving SSH unavailable.

Validation

• .venv/bin/python -m unittest discover -s tests -v
• bash -n linux/configure-ssh-operations.sh
• python3 tools/check-version-registry.py
• bash tools/check-external-protocol.sh