Add Hyprland and Greetd configurations; update desktop settings and user examples

hosts/common/optional/hyprland.nix

@@ -0,0 +1,18 @@
+{
+  config,
+  pkgs,
+  inputs,
+  ...
+}: {
+  programs.hyprland = {
+    enable = true;
+    # You can add more configuration options here as needed
+    # For example, to set a basic config file:
+    # settings = {
+    #   ...
+    # };
+    portalPackage = pkgs.xdg-desktop-portal-hyprland;
+  };
+
+  environment.sessionVariables.NIXOS_OZONE_WL = "1";
+}