fix: Don't eval surface kernel for all configs

hw/nix-surface.nix

@@ -17,12 +17,6 @@ with lib;
 
 let
   cfg = config.athenix.hw.nix-surface;
-  # Use older kernel version for better Surface Go compatibility
-  refSystem = inputs.nixpkgs-old-kernel.lib.nixosSystem {
-    system = pkgs.stdenv.hostPlatform.system;
-    modules = [ inputs.nixos-hardware.nixosModules.microsoft-surface-go ];
-  };
-  refKernelPackages = refSystem.config.boot.kernelPackages;
 in
 {
   imports = [
@@ -71,7 +65,13 @@ in
     ];
 
     # Use older kernel for better Surface hardware support
-    boot.kernelPackages = lib.mkForce refKernelPackages;
+    # Evaluated lazily - only when this module is enabled
+    boot.kernelPackages = lib.mkForce (
+      (inputs.nixpkgs-old-kernel.lib.nixosSystem {
+        system = pkgs.stdenv.hostPlatform.system;
+        modules = [ inputs.nixos-hardware.nixosModules.microsoft-surface-go ];
+      }).config.boot.kernelPackages
+    );
 
     # ========== Filesystem Configuration ==========
     athenix.host.filesystem.swapSize = lib.mkDefault "8G";