fix(power): coalesce charge-limit reapply events

USB-C power event bursts could repeatedly restart and SIGTERM the settling oneshot until systemd reached its start limit. Let successful runs return inactive and use coalescing start jobs for immediate and delayed reapplication.

Verified: V0 nix flake check --no-build, module parse, and git diff --check; V2 focused battery-charge-limit KVM test with a 12-event active-run burst. V3 hardware item #101 remains queued.

agent/MEMORY.md

@@ -77,7 +77,10 @@ iteration would otherwise rediscover.
   examples to crib from: `distro-id` (boots + `switch-to-configuration
   dry-activate`), `hardware-toggles` (kernel cmdline/PAM assertions),
   `battery-charge-limit` (fake Mains adapter via `test_power`, real udev
-  uevent, `InvocationID` change proves the restart).
+  event burst while the oneshot is active; clean inactive result plus an
+  `InvocationID` change proves coalesced AC re-apply). AC udev hooks for a
+  settling oneshot must use `start`, never `restart`: USB-C docks emit event
+  bursts and restarts SIGTERM the in-flight pass into `start-limit-hit`.
 - Themed-desktop screenshots work headlessly: software-GL Hyprland
   (`LIBGL_ALWAYS_SOFTWARE` on virtio-gpu) + `machine.screenshot()` QMP
   dump — prototyped 2026-06-19, kept as the fallback for theme previews