Add Steam and Vencord configurations: include desktop entries, session variables, and system packages

nixos/steam.nix

@@ -0,0 +1,13 @@
+{ ... }: {
+  programs.steam = {
+    enable = true;
+    gamescopeSession.enable = true;
+    remotePlay.openFirewall = true;
+    dedicatedServer.openFirewall = true;
+  };
+
+  hardware.graphics = {
+    enable = true;
+    enable32Bit = true;
+  };
+}

nixos/vencord.nix

@@ -0,0 +1,5 @@
+{ pkgs, ... }: {
+  environment.systemPackages = with pkgs; [
+    vencord
+  ];
+}