Add a `batterylimit` nomarchy-menu subcommand — a preset picker
(80/90/60/Off/Custom…) that writes settings.power.batteryChargeLimit via
theme-sync (--no-switch; lands on the next sys-rebuild, power.nix's oneshot
applies it). Surfaced as a first-class System row, self-gated on the
charge_control_end_threshold sysfs node like Power profile.
Moved out of the gum control-center (removed its Battery Limit case +
choose entry) so the toggle lives in one place — the rofi menu Bernardo
actually uses, per his request.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>