v0.3.0

Safety hardening release.\n\nChanges:\n- Avoid duplicate Port lines when existing sshd config already declares a port.\n- Back up and restore the hardening drop-in if sshd validation or restart fails.\n- Use fail2ban backend = systemd for modern Debian/Ubuntu images.\n- Automatically allow the new SSH port in UFW when UFW is active.\n- Poll for sshd listening ports after restart instead of sleeping once.\n- Require Bash 4+.\n- Match listening sockets more strictly against the sshd process.