Initial NixOS flake: Hyprland (end-4 illogical-impulse), NVIDIA, gaming, dev tools

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01C5ydBQk68JYw8HXzUDLAyV

modules/gaming.nix

@@ -0,0 +1,19 @@
+{ pkgs, ... }:
+
+{
+  programs.steam = {
+    enable = true;
+    remotePlay.openFirewall = true;
+    gamescopeSession.enable = true; # "Steam (gamescope)" session in SDDM
+    extraCompatPackages = [ pkgs.proton-ge-bin ];
+  };
+
+  programs.gamemode.enable = true;
+  programs.gamescope.enable = true;
+  # programs.gamescope.capSysNice = true; # left off — known to break gamescope under Steam
+
+  environment.systemPackages = with pkgs; [
+    mangohud
+    protonup-qt
+  ];
+}