feat(control-center): battery charge-limit as a preset toggle

The "Battery Limit" entry was a raw number prompt; make it a proper
toggle picker — Off / 80% (recommended) / 90% / 60% / Custom… — writing
settings.power.batteryChargeLimit. Kept in the control-center, where the
baked rebuild-valued System Toggles live (the rofi nomarchy-menu is the
instant surface; the CC holds config values), and reachable from the menu
via System › Control Center. Base machinery (the sysfs oneshot + AC-replug
udev in power.nix) is unchanged, so it lands on the next sys-rebuild like
its siblings.

Instant-effect (no rebuild) is refiled in BACKLOG § PROPOSED as
[blocked:hw]: it needs a udev-writable threshold node, confirmable only on
a laptop with the control.

Verified: V0 (bash -n; nix flake check --no-build, green) + V1
(nomarchy-control-center package builds — the writeShellApplication
shellcheck gate passes). Session spot-check queued in HARDWARE-QUEUE.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

agent/JOURNAL.md

@@ -17,6 +17,27 @@ Template:
 
 ---
 
+## 2026-07-07 — Battery charge-limit quick toggle (iteration #55)
+- **Task:** BACKLOG PROPOSED (promoted by Bernardo) — a toggle for the
+  battery charge threshold.
+- **Did:** Replaced the control-center "Battery Limit" raw number-prompt
+  with a preset toggle picker (Off / 80% recommended / 90% / 60% /
+  Custom…) writing `settings.power.batteryChargeLimit`. Kept it in the
+  control-center — that's where the baked, rebuild-valued System Toggles
+  live (rofi `nomarchy-menu` is the *instant* surface; the CC holds
+  config values); it's reachable from the menu via System › Control
+  Center. Base machinery (sysfs oneshot + AC-replug udev in power.nix)
+  untouched.
+- **Verified:** V0 (`bash -n`; `nix flake check --no-build`, green) + V1
+  (nomarchy-control-center package builds → the writeShellApplication
+  shellcheck gate passes).
+- **Pending:** instant-effect (no rebuild) refiled in PROPOSED as
+  `[blocked:hw]` — needs a udev-writable sysfs node, confirmable only on
+  a laptop with the charge-threshold control. Light session spot-check
+  queued in HARDWARE-QUEUE.
+- **Next suggestion:** item 29 is `[human]`/`[blocked:hw]`; remaining is
+  item 28 slices or a QA sweep.
+
 ## 2026-07-07 — Waybar overlaps fullscreen video (iteration #54)
 - **Task:** BACKLOG item 30 — bar drawn on top of a fullscreen YouTube video.
 - **Did:** `layer: top` → `bottom` in the generated `waybar.nix` and the