update-platform-binary.sh: the last two lines it needs

After the carlos-restart.path block, guarded the same way:

if [ -f /etc/systemd/system/carlos-system-update.path ]; then systemctl enable --now carlos-system-update.path systemctl enable carlos-system-recover.service fi

And to the post-conditions at the end:

systemctl is-active carlos-system-update.path systemctl is-enabled carlos-system-recover.service

Same change in amadan.net/tito/carlos-infrastructure/scripts/update-platform-binary.sh. After every deployment has been hand-rolled once onto a binary carrying the system-update spec, the script is retired (spec §10).