feature(greeter): replace sddm with greetd since sddm has issues with rdna4

modules/nixos/greetd.nix

@@ -0,0 +1,14 @@
+{ config, lib, pkgs, ... }:
+
+{
+  # greetd display manager with tuigreet
+  services.greetd = {
+    enable = true;
+    settings = {
+      default_session = {
+        command = "${pkgs.greetd.tuigreet}/bin/tuigreet --time --cmd niri-session";
+        user = "greeter";
+      };
+    };
+  };
+}