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>

modules/home/waybar.nix

@@ -228,7 +228,14 @@ in
 {
   programs.waybar = lib.mkIf config.nomarchy.waybar.enable {
     enable = true;
-    systemd.enable = true; # started/stopped with graphical-session.target
+    # Launched from Hyprland's exec-once (hyprland.nix), NOT a systemd user
+    # service. Bound to graphical-session.target the unit raced Hyprland's IPC
+    # on a warm relogin — it started before the socket was up, exited, landed
+    # in `failed`, and was never retried, so the bar vanished. exec-once only
+    # fires once Hyprland is up, dodging the race; theme switches reload the
+    # running bar via SIGUSR2 (nomarchy-theme-sync). No uwsm here to manage the
+    # session target, so we don't depend on its lifecycle.
+    systemd.enable = false;
 
     # mkDefault so downstream can replace the whole bar config/style with
     # a plain home.nix assignment. For per-theme identity, prefer the