Update to (somewhat?) dendritic pattern

Heavily inspired by https://github.com/Doc-Steve/dendritic-design-with-flake-parts.

> Atomic commits? Never heard of them!

modules/programs/steam.nix

@@ -0,0 +1,16 @@
+{
+  flake.modules.nixos.steam = { pkgs, ... }: {
+    programs.steam = {
+      enable = true;
+      extraCompatPackages = [
+        pkgs.proton-ge-bin
+      ];
+      protontricks = {
+        enable = true;
+      };
+      dedicatedServer.openFirewall = true;
+      localNetworkGameTransfers.openFirewall = true;
+      remotePlay.openFirewall = true;
+    };
+  };
+}