fix(waybar): launch from exec-once, not a systemd user service

Waybar vanished after a logout→login (no reboot): the bar's systemd user
service landed in `failed`. HM's Hyprland integration cycles
hyprland-session.target on every launch (exec-once stop && start), which
re-pulls WantedBy units — including waybar.service — very early, before
Hyprland's IPC socket is ready. Waybar's hyprland/workspaces & window
modules can't connect, so it exits non-zero and is never retried. A cold
boot's extra latency hid the race, so it only bit on warm relogins. The
non-IPC session services (swaync/hypridle/hyprsunset) survive the same
cycling fine, which is why night-light kept working.

Launch waybar from Hyprland's own exec-once instead (systemd.enable =
false). exec-once entries are dispatched once the compositor is up, so the
IPC socket is ready — the same reliable pattern awww-daemon, the wallpaper
sync and the keyboard watcher already use across relogins. Since the unit
no longer exists to be restarted on a home-manager switch, nudge the
running bar to re-read its rebuilt config/style with SIGUSR2 from
nomarchy-theme-sync so theme switches still reapply the bar live.

Found on the Latitude 5410 hardware sweep (systemctl --user status showed
waybar.service loaded/failed; manual start worked).

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

pkgs/nomarchy-theme-sync/nomarchy-theme-sync.py

@@ -171,6 +171,11 @@ def run_switch() -> None:
         notify("Theme rebuild FAILED — see terminal / journal", urgency="critical")
         die("rebuild failed (state file already updated; fix and re-run)")
     notify("Theme applied ✓")
+    # Waybar runs from Hyprland's exec-once (not a systemd unit HM would restart
+    # on switch), so nudge the running bar to re-read its freshly rebuilt
+    # config/style. SIGUSR2 = reload; harmless no-op if waybar isn't running.
+    if shutil.which("pkill"):
+        subprocess.run(["pkill", "--signal", "SIGUSR2", "-x", "waybar"], check=False)
 
 
 # ─── Theme assets (wallpapers) ────────────────────────────────────────────