Give neogaia the CachyOS kernel and hardware enablement

Select the CachyOS kernel per-Host via boot.kernelPackages, enable Intel
microcode and redistributable firmware (ath10k for the QCA6174 wifi), and
move zram behind a toggle Module. Declare the chaotic binary cache in the
base Nix settings (extra-substituters/keys) so the built system fetches the
kernel from nyx-cache rather than compiling it.

hosts/neogaia/default.nix

@@ -1,4 +1,4 @@
-{ ... }:
+{ pkgs, ... }:
 # neogaia — Dell XPS 13 9380 laptop.
 #
 # The disk layout lives in ./disk.nix (disko); the resulting `fileSystems` are
@@ -17,6 +17,19 @@
   boot.loader.systemd-boot.enable = true;
   boot.loader.efi.canTouchEfiVariables = true;
 
-  # Swap is RAM-backed zram rather than an on-disk partition.
-  zramSwap.enable = true;
+  # Kernel is a per-Host choice, expressed through boot.kernelPackages: neogaia
+  # runs the CachyOS kernel from chaotic-nyx (fetched from the chaotic binary
+  # cache wired in system/, not compiled from source). Other Hosts pick their
+  # own kernel the same way, so the choice never leaves the Host.
+  boot.kernelPackages = pkgs.linuxPackages_cachyos;
+
+  # Intel CPU microcode updates for the XPS 13's Core i7-8565U.
+  hardware.cpu.intel.updateMicrocode = true;
+
+  # Redistributable firmware — carries the ath10k blobs the QCA6174 wifi needs.
+  hardware.enableRedistributableFirmware = true;
+
+  # Swap is RAM-backed zram (the zram Module) rather than an on-disk partition,
+  # matching the disko layout, which declares no swap partition.
+  modules.zram.enable = true;
 }