add steam runtime to thinkpad

hosts/nixos/thinkpad/system.nix

@@ -1,4 +1,19 @@
-{ config, pkgs, lib, ... }: {
+{ config, pkgs, lib, ... }:
+
+let
+  # Helper function to patch desktop entries for NVIDIA offload
+  patchDesktop = pkg: appName: from: to: lib.hiPrio (
+    pkgs.runCommand "patched-desktop-entry-for-${appName}" {} ''
+      ${pkgs.coreutils}/bin/mkdir -p $out/share/applications
+      ${pkgs.gnused}/bin/sed 's#${from}#${to}#g' < ${pkg}/share/applications/${appName}.desktop > $out/share/applications/${appName}.desktop
+    ''
+  );
+
+  # Wrapper to automatically run applications with NVIDIA offload
+  GPUOffloadApp = pkg: desktopName: patchDesktop pkg desktopName "^Exec=" "Exec=nvidia-offload ";
+in
+
+{
   imports = [
     ./hardware-configuration.nix
     ./containers.nix  # Host-specific container definitions
@@ -119,6 +134,21 @@
   services.displayManager.gdm.enable = true;
   services.desktopManager.gnome.enable = true;
 
+  # Enable NVIDIA video drivers
+  services.xserver.videoDrivers = [ "nvidia" ];
+
+  # Steam gaming configuration
+  programs.steam = {
+    enable = true;
+    remotePlay.openFirewall = true;
+    dedicatedServer.openFirewall = true;
+    localNetworkGameTransfers.openFirewall = true;
+    gamescopeSession.enable = true;
+  };
+
+  # Enable GameMode for performance optimization
+  programs.gamemode.enable = true;
+
   # Keyboard layout
   services.xserver.xkb = {
     layout = "us";
@@ -266,6 +296,14 @@
     # ThinkPad specific
     lm_sensors  # Temperature monitoring
     smartmontools  # Disk health monitoring (SMART)
+
+    # Gaming utilities
+    mangohud  # Performance overlay for games
+    gamescope  # SteamOS session compositing window manager
+    protonup-qt  # Proton version manager
+
+    # Steam with NVIDIA offload (patched desktop entry)
+    (GPUOffloadApp config.programs.steam.package "steam")
   ];