feat(services): run quickshell as a user service

Mirrors the unit moonarch now ships. spawn-at-startup never restarted it, so a
crash cost the bar for the rest of the session.

modules/services.nix

@@ -96,6 +96,21 @@
     };
   };
 
+  # The bar, launcher and every popout. A unit rather than a spawn-at-startup so
+  # a crash does not leave the session without a bar until the next login.
+  systemd.user.services.quickshell = {
+    description = "Quickshell bar and shell";
+    partOf = [ "graphical-session.target" ];
+    after = [ "graphical-session.target" ];
+    wantedBy = [ "graphical-session.target" ];
+    serviceConfig = {
+      Type = "simple";
+      ExecStart = "${lib.getExe pkgs.quickshell} -c moonarch";
+      Restart = "on-failure";
+      RestartSec = 3;
+    };
+  };
+
   # nixpkgs ships the package but no module, and the package carries no unit of
   # its own, so it is declared here. Mirrors /usr/lib/systemd/user/stasis.service.
   systemd.user.services.stasis = {