nix: replace greetd with SDDM

modules/linux/login.nix

@@ -1,17 +1,20 @@
 { config, lib, pkgs, ... }:
 
 {
-  # display manager
-  services.greetd = {
+  services.displayManager.sddm = {
     enable = true;
-    settings = {
-      initial_session = {
-        command = "uwsm start default";
-        user = "nico";
-      };
-      default_session = {
-        command = "${pkgs.greetd.tuigreet}/bin/tuigreet --time --greet-align left";
-      };
-    };
+    wayland.enable = true;
+    theme = "where_is_my_sddm_theme_qt5";
   };
+
+  environment.systemPackages = with pkgs; [
+    (pkgs.where-is-my-sddm-theme.override {
+      variants = [ "qt5" ];
+      themeConfig.General = {
+        background = pkgs.nixos-artwork.wallpapers.nineish-dark-gray.gnomeFilePath;
+        backgroundMode = "fill";
+        cursorColor = "#ffffff";
+      };
+   })
+  ];
 }