fix(stasis): let the desktop suspend on idle again

moonarch 7a24cdb puts a suspend step back into the desktop plan; it was lost
when that plan stopped inheriting the ac: blocks. systemctl has to be on the
unit PATH for it, or the step fails silently like swaylock did.

flake.lock

@@ -24,11 +24,11 @@
     "moonarch": {
       "flake": false,
       "locked": {
-        "lastModified": 1788284005,
-        "narHash": "sha256-jrJ6gZl/DPK3lLxu27pUDsr8CXQ/fe7uXZn1s4/k5Yw=",
+        "lastModified": 1788955787,
+        "narHash": "sha256-VII5Od3i1YyHqIWJgDb2El58Xf2XgCdcnfRNzmz0ueg=",
         "ref": "refs/heads/main",
-        "rev": "b94cc567c5796f6f2c79740c0adbe49d9da895b3",
-        "revCount": 176,
+        "rev": "7a24cdb6ae1831ffe74c54f1bce1d3538147284f",
+        "revCount": 178,
         "type": "git",
         "url": "https://gitea.moonarch.de/nevaforget/moonarch.git"
       },

modules/services.nix

@@ -189,6 +189,7 @@ in
       libnotify
       swaylock
       brightnessctl
+      systemd
     ];
     # No waylandClientHardening: swaylock is a child of this unit and
     # authenticates through the setuid-root unix_chkpwd. `systemd --user` builds