use jovian-nixos + fixup niri display session handling

etcnixos/system-mreow.nix

@@ -34,4 +34,25 @@
   # disable framework kernel module
   # https://github.com/NixOS/nixos-hardware/issues/1330
   hardware.framework.enableKmod = false;
+
+  # Greetd display manager
+  services.greetd = {
+    enable = true;
+    settings = {
+      default_session = {
+        command = "${lib.getExe pkgs.tuigreet} --sessions /etc/xdg/wayland-sessions/ --time";
+        user = username;
+      };
+      terminal.vt = lib.mkForce 2;
+    };
+  };
+
+  environment.etc."xdg/wayland-sessions/niri-session.desktop".text = ''
+    [Desktop Entry]
+    Name=Niri Session
+    Comment=Niri Wayland compositor
+    Exec=niri-session
+    Type=Application
+    DesktopNames=niri
+  '';
 }