gaming: flesh out gaming module

Move the gaming module from home-manager to nixos and flesh it out with
additional installs, such as steam.

hosts/desktop/configuration.nix

@@ -7,6 +7,7 @@
     impermanence.enable = true;
     impermanence.wipeOnBoot = true;
     flatpak.enable = true;
+    gaming.enable = true;
   };
 
   imports = with inputs.hardware.nixosModules; [

hosts/desktop/home.nix

@@ -1,6 +1,5 @@
 { lib, ... }: {
   custom = {
-    gaming = true;
     editors.vscode = true;
     editors.idea = true;
     gnome.favorites = lib.mkAfter [

hosts/matebook/home.nix

@@ -1,6 +1,5 @@
 { ... }: {
   custom = {
-    gaming = true;
     editors.vscode = true;
     editors.idea = true;
   };

modules/nixos/games.nix

@@ -0,0 +1,36 @@
+{ config, lib, pkgs, ... }:
+let
+  cfg = config.custom.gaming;
+in
+{
+  options.custom.gaming.enable = lib.mkEnableOption "gaming";
+
+  config = lib.mkIf cfg.enable {
+    programs.steam = {
+      enable = true;
+      protontricks.enable = true;
+      remotePlay.openFirewall = true;
+      localNetworkGameTransfers.openFirewall = true;
+      extraCompatPackages = with pkgs; [
+        proton-ge-bin
+      ];
+    };
+
+    programs.nix-ld = {
+      enable = true;
+      libraries = pkgs.steam-run.fhsenv.args.multiPkgs pkgs;
+    };
+
+    environment.systemPackages = with pkgs; [
+      heroic
+      prismlauncher
+      steam-run
+    ];
+
+    nixpkgs.config.allowUnfreePredicate = pkg: lib.elem (lib.getName pkg) [
+      "steam"
+      "steam-original"
+      "steam-run"
+    ];
+  };
+}