feat: Nomarchy ground-up rewrite on NixOS 26.05

Full replacement of the previous iteration, rebuilt around three ideas:

- Pure evaluation: theme-state.json lives inside the flake and is read
  via the nomarchy.stateFile option — no --impure, ever.
- All-Home-Manager theming: `nomarchy-theme-sync apply` writes the JSON
  and runs `home-manager switch`; every theme change is one atomic,
  rollbackable generation. Wallpaper (swww) is the sole runtime piece.
- Flat, downstream-first layout: modules/{nixos,home} with one
  options.nix each, exported as nixosModules/homeModules + overlay +
  flake template; system (nixos-rebuild) and desktop (home-manager
  switch) rebuild paths are fully split.

Ships 21 themes imported from the previous iteration (palettes,
wallpapers, btop themes, six whole-swap Waybar identities), Stylix for
the GTK/Qt/cursor long tail, a live ISO target with offline theme
switching, and docs/TESTING.md with the QEMU verification workflow.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

hosts/default/configuration.nix

@@ -0,0 +1,24 @@
+# Reference host — machine specifics ONLY.
+# The distro itself comes from nixosModules.nomarchy (modules/nixos),
+# imported in flake.nix. Keep this file boring.
+{ pkgs, username, ... }:
+
+{
+  imports = [ ./hardware-configuration.nix ];
+
+  boot.loader.systemd-boot.enable = true;
+  boot.loader.efi.canTouchEfiVariables = true;
+  boot.kernelPackages = pkgs.linuxPackages_latest;
+
+  networking.hostName = "nomarchy";
+  time.timeZone = "UTC"; # adjust per machine
+  i18n.defaultLocale = "en_US.UTF-8";
+
+  users.users.${username} = {
+    isNormalUser = true;
+    description = "Nomarchy user";
+    extraGroups = [ "wheel" "networkmanager" "video" "input" ];
+  };
+
+  system.stateVersion = "26.05";
+}

hosts/default/hardware-configuration.nix

@@ -0,0 +1,15 @@
+# PLACEHOLDER — replace with the output of `nixos-generate-config` on the
+# target machine. The mkDefault values below only exist so the flake
+# evaluates and `nix flake check` passes before first install.
+{ lib, ... }:
+
+{
+  boot.initrd.availableKernelModules = lib.mkDefault [ "xhci_pci" "ahci" "nvme" "usbhid" "sd_mod" ];
+
+  fileSystems."/" = lib.mkDefault {
+    device = "/dev/disk/by-label/nixos";
+    fsType = "ext4";
+  };
+
+  nixpkgs.hostPlatform = lib.mkDefault "x86_64-linux";
+}