Add initial support for Steam Deck

nixos/deck/greetd-steam.nix

@@ -0,0 +1,19 @@
+{pkgs, ...}: {
+  services = {
+    # Configure greetd for "auto" login (single user only)
+    greetd = {
+      enable = true;
+      restart = true;
+      settings = {
+        terminal = {
+          vt = 2;
+          switch = true;
+        };
+        default_session = {
+          command = "start-gamescope-session";
+          user = "jimbo";
+        };
+      };
+    };
+  };
+}

nixos/deck/jovian.nix

@@ -0,0 +1,15 @@
+{
+  imports = [
+    ./greetd-steam.nix
+  ];
+
+  jovian = {
+    steam = {
+      enable = true;
+      desktopSession = "sway";
+    };
+    decky-loader.enable = true;
+    devices.steamdeck.enable = true;
+    steamos.useSteamOSConfig = true;
+  };
+}