Add NixOS configuration for john-endesktop ZFS/NFS server

Create configuration to migrate john-endesktop from Arch Linux to NixOS while
maintaining existing ZFS pools (media JBOD and swarmvols mirror) and NFS
exports for k3s cluster.

Configuration includes:
- ZFS support with automatic pool import
- NFS server exporting both pools to 10.0.0.0/24
- Correct ZFS hostid (007f0101) to resolve hostid warnings
- Btrfs root filesystem on nvme0n1p5 (810GB)
- Comprehensive migration plan with rollback procedures

The migration is designed to be safe with Arch Linux remaining bootable
as a fallback until NixOS is verified stable.

machines/john-endesktop/hardware-configuration.nix

@@ -0,0 +1,48 @@
+# Hardware configuration for john-endesktop
+# This file should be regenerated after NixOS installation using:
+# nixos-generate-config --show-hardware-config
+
+{ config, lib, pkgs, modulesPath, ... }:
+
+{
+  imports = [
+    (modulesPath + "/installer/scan/not-detected.nix")
+  ];
+
+  # Boot configuration
+  boot.initrd.availableKernelModules = [ "xhci_pci" "ahci" "nvme" "usbhid" "usb_storage" "sd_mod" ];
+  boot.initrd.kernelModules = [ ];
+  boot.kernelModules = [ "kvm-intel" ];
+  boot.extraModulePackages = [ ];
+
+  # File systems - these will need to be updated after installation
+  # The nvme0n1p5 partition will be formatted as btrfs for NixOS root
+  fileSystems."/" = {
+    # Update this device path after installation
+    device = "/dev/disk/by-uuid/CHANGE-THIS-TO-YOUR-UUID";
+    fsType = "btrfs";
+    options = [ "subvol=@" "compress=zstd" "noatime" ];
+  };
+
+  fileSystems."/boot" = {
+    # This should match your current EFI partition
+    device = "/dev/disk/by-uuid/F5C6-D570";
+    fsType = "vfat";
+    options = [ "fmask=0022" "dmask=0022" ];
+  };
+
+  # ZFS pools - these are imported by ZFS, not managed by fileSystems
+  # The pools should be imported automatically via boot.zfs.extraPools
+  # /media and /swarmvols will be mounted by ZFS
+
+  # Swap - using ZFS zvol
+  swapDevices = [
+    { device = "/dev/zvol/media/swap"; }
+  ];
+
+  # CPU microcode
+  hardware.cpu.intel.updateMicrocode = lib.mkDefault config.hardware.enableRedistributableFirmware;
+
+  # Networking
+  networking.useDHCP = lib.mkDefault true;
+}