fix(services): give quickshell the session path

As a spawn-at-startup it inherited niri's environment; the unit got systemd's
minimal one, so every widget that shells out failed to start its process --
niri, nmcli, powerprofilesctl, the moonarch scripts and a dozen more.

modules/services.nix

@@ -1,7 +1,7 @@
 # ABOUTME: systemd system and user services for the desktop session.
 # ABOUTME: Rebuilt from moonarch/defaults/etc/systemd/, whose units use FHS paths.
 
-{ pkgs, lib, moonarchPkgs, ... }:
+{ config, pkgs, lib, moonarchPkgs, ... }:
 
 {
   # --- Audio ---
@@ -103,6 +103,11 @@
     partOf = [ "graphical-session.target" ];
     after = [ "graphical-session.target" ];
     wantedBy = [ "graphical-session.target" ];
+    # The widgets shell out to niri, nmcli, powerprofilesctl, the moonarch
+    # scripts and a dozen more, and which ones is a property of the QML, not of
+    # this file. As a spawn-at-startup it inherited the session PATH; the unit
+    # gets the same set rather than a list that goes stale on the next widget.
+    path = [ config.system.path ];
     serviceConfig = {
       Type = "simple";
       ExecStart = "${lib.getExe pkgs.quickshell} -c moonarch";