The oneUpPower kernel module powered the system off at low SOC, but the
icon now reads the battery over I2C and no longer relies on that module.
Restore the safety net in the icon itself.
While running on battery, warn via a tray notification at <=10% and run
`systemctl poweroff` at <=5%. systemctl poweroff is authorised for the
active desktop session without sudo (logind CanPowerOff returns "yes").
State resets when AC is reconnected.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
2e65dadfa9