feat(pikachu): add initial NixOS host

hosts/pikachu/default.nix

@@ -0,0 +1,58 @@
+{
+  config,
+  pkgs,
+  ...
+}:
+# pikachu — AZW ME Pro server.
+# Disk layout is in ./disk.nix.
+# `fileSystems` for the root disk are derived from it.
+{
+  imports = [
+    ./hardware-configuration.nix
+    ./disk.nix
+  ];
+
+  system.stateVersion = "26.05";
+
+  boot.loader.systemd-boot.enable = true;
+  boot.loader.efi.canTouchEfiVariables = true;
+
+  hardware.cpu.intel.updateMicrocode = true;
+  hardware.enableRedistributableFirmware = true;
+
+  zramSwap.enable = true;
+
+  systemd.network = {
+    enable = true;
+    networks."10-uplink" = {
+      matchConfig.MACAddress = "78:55:36:07:af:49";
+      networkConfig.DHCP = "yes";
+      linkConfig.RequiredForOnline = "routable";
+    };
+  };
+  networking.useDHCP = false;
+
+  boot.zfs.forceImportRoot = false;
+
+  modules.zfs = {
+    enable = true;
+    hostId = "2346edbd";
+    pools.pikachu = { };
+  };
+
+  modules.ssh.enable = true;
+  modules.ssh.hostKeys.restore = false;
+  modules.ssh.authorizedKeys = config.modules.ssh.workstationKeys;
+
+  modules.git.enable = true;
+  modules.toolkit.enable = true;
+
+  environment.systemPackages = with pkgs; [
+    pciutils
+    smartmontools
+    usbutils
+  ];
+
+  time.timeZone = "America/New_York";
+  i18n.defaultLocale = "en_GB.UTF-8";
+}

hosts/pikachu/disk.nix

@@ -0,0 +1,32 @@
+{ ... }:
+# pikachu's install layout for disko: one NVMe boot disk with an EFI system partition and ext4 root.
+# The existing 8 TB ZFS mirror is imported by name and is never declared here.
+{
+  disko.devices.disk.main = {
+    type = "disk";
+    device = "/dev/nvme0n1";
+    content = {
+      type = "gpt";
+      partitions = {
+        ESP = {
+          size = "2G";
+          type = "EF00";
+          content = {
+            type = "filesystem";
+            format = "vfat";
+            mountpoint = "/boot";
+            mountOptions = [ "umask=0077" ];
+          };
+        };
+        root = {
+          size = "100%";
+          content = {
+            type = "filesystem";
+            format = "ext4";
+            mountpoint = "/";
+          };
+        };
+      };
+    };
+  };
+}

hosts/pikachu/hardware-configuration.nix

@@ -0,0 +1,18 @@
+{ lib, modulesPath, ... }:
+# Hardware detected from the Proxmox inventory for this machine.
+# disko derives the root disk filesystems, none declared here.
+{
+  imports = [ (modulesPath + "/installer/scan/not-detected.nix") ];
+
+  boot.initrd.availableKernelModules = [
+    "ahci"
+    "nvme"
+    "sd_mod"
+    "xhci_pci"
+  ];
+  boot.initrd.kernelModules = [ ];
+  boot.kernelModules = [ "kvm-intel" ];
+  boot.extraModulePackages = [ ];
+
+  nixpkgs.hostPlatform = lib.mkDefault "x86_64-linux";
+}