feat: use linux zen for desktop

flake.nix

@@ -3,17 +3,17 @@
 
   nixConfig = {
     extra-substituters = [
+      "https://cache.rgbcu.be/"
       "https://cache.garnix.io/"
       "https://cache.privatevoid.net"
-      "https://cache.rgbcu.be/"
       "https://hyprland.cachix.org/"
       "https://nix-community.cachix.org/"
     ];
 
     extra-trusted-public-keys = [
+      "cache.rgbcu.be:nBN/5Qg5E8GIYwaoslm9DYo2zeqlBiCVNCPf17djr+w="
       "cache.garnix.io:CTFPyKSLcx5RMJKfLo5EEPUObbA78b0YQ2DTCJXqr9g="
       "cache.privatevoid.net:SErQ8bvNWANeAvtsOESUwVYr2VJynfuc9JRwlzTTkVg="
-      "cache.rgbcu.be:nBN/5Qg5E8GIYwaoslm9DYo2zeqlBiCVNCPf17djr+w="
       "hyprland.cachix.org-1:a7pgxzMz7+chwVL3/pzj6jIBMioiJM7ypFP8PwtkuGc="
       "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
     ];

modules/linux/kernel.nix

@@ -1,5 +1,8 @@
-{ pkgs, ... }: {
-  boot.kernelPackages = pkgs.linuxPackages_latest;
+{ config, pkgs, ... }: {
+  boot.kernelPackages = if config.isServer then
+    pkgs.linuxPackages_latest
+  else
+    pkgs.linuxKernel.packages.linux_zen;
 
   # Credits:
   # - https://github.com/NotAShelf/nyx/blob/main/modules/core/common/system/security/kernel.nix