revert(live-sync): drop path-activation unit

Frank veto: DirectoryNotEmpty re-fires on every file event (GUI writes,
wallpaper shuffle) un-debounced -> hundreds of heartbeat spawns/day.
The sweep is cheap (57 ms CPU) but the trigger design was event spam.
Exposure-window fix is an open design question; timer unchanged.

dotfiles/systemd-user/.config/systemd/user/live-sync.path

@@ -1,13 +0,0 @@
-[Unit]
-Description=Fire the live-sync heartbeat within seconds of a dotfiles-tier write
-
-[Path]
-# GUI writes (noctalia settings.toml, niri cfg) land in the repo via the
-# dotfiles symlinks; this directory watch makes "GUI edit -> durable commit"
-# sub-second instead of up to one heartbeat interval. DirectoryNotEmpty fires
-# while the dir holds any file, so the unit re-triggers on every modification
-# (the empty-dir edge case is irrelevant here — dotfiles is never empty).
-DirectoryNotEmpty=%h/.omp/dotfiles
-
-[Install]
-WantedBy=paths.target