feat(battery): low-battery notifications at the bar's 25/10% thresholds (item 13 slice)

The bar colored the battery at 25/10% but nothing notified. New
shellcheck-gated watcher (pkgs/nomarchy-battery-notify, overlay) polls
the same sysfs the bar reads — type=Battery, scope!=Device — and fires
one toast per downward crossing (normal at 25%, critical at 10%; swaync
keeps critical up until dismissed), re-armed by charging. Self-gates on
battery presence (the powerprofile pattern), so desktops get a silent
no-op. HM user unit behind nomarchy.batteryNotify.enable (default on)
with libnotify on the unit PATH; notify-send resolves from PATH so the
VM check can shim it. poweralertd rejected: its UPower thresholds
(20/5) wouldn't match the bar, and it toasts every plug/unplug.

Verified: V0 (flake check, bash -n); V1 (template-home builds, unit in
the generation); V2 GREEN (new checks.battery-notify, test_power fake
battery: self-gate, silence at 80%, one toast per crossing, critical
urgency, charging re-arms). Remains: V3 — real swaync toast on a
draining laptop (HARDWARE-QUEUE).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

agent/JOURNAL.md

@@ -17,6 +17,28 @@ Template:
 
 ---
 
+## 2026-07-05 — low-battery notifications (iteration #24, item 13 slice)
+- **Task:** BACKLOG NEXT#13 second slice — the bar colors the battery
+  at 25/10% but nothing *notified*.
+- **Did:** pkgs/nomarchy-battery-notify (shellcheck-gated watcher:
+  polls the same sysfs the bar reads — type=Battery, scope≠Device —
+  one toast per downward crossing: normal@25, critical@10; re-armed by
+  charging; self-gates on battery presence → desktop no-op) + overlay.
+  HM unit in modules/home/battery-notify.nix behind
+  nomarchy.batteryNotify.enable (default on), graphical-session-bound,
+  libnotify on the unit PATH (notify-send resolved from PATH so the
+  check can shim it). README row. Chose the tiny watcher over
+  poweralertd: its UPower thresholds (20/5) wouldn't match the bar,
+  and it toasts every plug/unplug.
+- **Verified:** V0; V1 — template-home builds, unit present; V2 GREEN —
+  new checks.battery-notify (test_power fake battery): self-gate exits
+  0 without a battery, silence at 80%, exactly one low toast crossing
+  25, one critical-urgency toast crossing 10, charging re-arms → a
+  second drain toasts again.
+- **Pending:** V3 queued (real toast through swaync while draining).
+- **Next suggestion:** item 13 final slice — hyprpicker color picker
+  (Tools › entry + SUPER+CTRL bind).
+
 ## 2026-07-04 — caffeine/idle-inhibit toggle (iteration #23, item 13 slice)
 - **Task:** BACKLOG NEXT#13 first slice — idle_inhibitor in the
   generated bar (summer-night had it; reverse parity gap).