feat(rofi): battery charge-limit toggle in the System menu

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>

agent/BACKLOG.md

@@ -34,13 +34,11 @@ Hyprland bind's modmask/keysym against the *actual* layout, whether rofi
 2.0.0 changed anything, and that the cheatsheet path still resolves.
 
 
-### 36. Battery / power quick menu
-(Raised by Bernardo, 2026-07-07 — items "battery toggle in a rofi
-submenu" + item 6.) Two slices:
-- (a) **Move the charge-threshold toggle into the rofi System submenu.**
-  Iteration #55 put it in the gum control-center; Bernardo wants it as a
-  first-class row in `nomarchy-menu` › System (self-gated on the
-  `charge_control_end_threshold` sysfs node), reusing the preset picker.
+### 36. Battery / power quick menu `[human]`
+(Raised by Bernardo, 2026-07-07 — item 6.) Slice (a) — the charge-threshold
+toggle in the rofi System submenu — shipped 2026-07-07 (iteration #64;
+`nomarchy-menu batterylimit`, self-gated on the sysfs node, and MOVED out
+of the gum control-center). Remaining:
 - (b) `[human]` **Battery-icon click → a dedicated power menu** offering
   charge threshold + power profile (and switching backend to TLP when
   relevant). Bernardo will provide a mockup ("when it's time") — hold