Wire stasis into the desktop and add its user service

Upstream ships a systemd unit in the Arch package but not in the source
tarball, so it is declared in the module.

modules/desktop.nix

@@ -164,6 +164,7 @@ in
     moonarchPkgs.moonlock
     moonarchPkgs.moonset
     moonarchPkgs.sweet-cursors
+    moonarchPkgs.stasis
     moonarch-scripts
 
     # Compositor extras

modules/services.nix

@@ -1,7 +1,7 @@
 # ABOUTME: systemd user and system services for the Moonarch session.
 # ABOUTME: Rebuilt from defaults/etc/systemd/ because the units use FHS paths.
 
-{ pkgs, lib, ... }:
+{ pkgs, lib, moonarchPkgs, ... }:
 
 {
   # --- Audio ---
@@ -45,6 +45,22 @@
     };
   };
 
+  # Upstream ships a unit in the Arch package but not in the tarball, so it is
+  # declared here. Mirrors /usr/lib/systemd/user/stasis.service.
+  systemd.user.services.stasis = {
+    description = "Stasis Wayland Idle Manager";
+    partOf = [ "graphical-session.target" ];
+    after = [ "graphical-session.target" ];
+    wantedBy = [ "graphical-session.target" ];
+    serviceConfig = {
+      Type = "simple";
+      ExecStart = "${lib.getExe moonarchPkgs.stasis}";
+      ExecReload = "${lib.getExe moonarchPkgs.stasis} reload";
+      Restart = "on-failure";
+      RestartSec = 2;
+    };
+  };
+
   systemd.user.services.cliphist-text = {
     description = "Clipboard history manager (text)";
     partOf = [ "graphical-session.target" ];