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>

templates/downstream/flake.nix

@@ -0,0 +1,53 @@
+{
+  description = "My Nomarchy machine";
+
+  inputs = {
+    # Pin Nomarchy; nixpkgs and home-manager follow whatever it ships.
+    nomarchy.url = "github:YOUR-USER/nomarchy"; # <- point at the distro repo
+    nixpkgs.follows = "nomarchy/nixpkgs";
+    home-manager.follows = "nomarchy/home-manager";
+  };
+
+  outputs = { self, nomarchy, nixpkgs, home-manager, ... }:
+    let
+      system = "x86_64-linux";
+      username = "me"; # <- your login name
+
+      pkgs = import nixpkgs {
+        inherit system;
+        overlays = [ nomarchy.overlays.default ];
+      };
+    in
+    {
+      # System layer — rebuilt rarely:
+      #   sudo nixos-rebuild switch --flake .#default
+      nixosConfigurations.default = nixpkgs.lib.nixosSystem {
+        inherit system;
+        modules = [
+          nomarchy.nixosModules.nomarchy   # the distro
+          ./hardware-configuration.nix     # from `nixos-generate-config`
+          ./system.nix                     # your machine
+        ];
+      };
+
+      # Desktop layer — rebuilt on every theme change, no sudo:
+      #   home-manager switch --flake .#me
+      # (`nomarchy-theme-sync apply <theme>` runs this for you.)
+      homeConfigurations.${username} = home-manager.lib.homeManagerConfiguration {
+        inherit pkgs;
+        modules = [
+          nomarchy.homeModules.nomarchy
+          ./home.nix
+          {
+            # Your theme state — written by nomarchy-theme-sync, baked
+            # in on every switch. Keep it git-tracked.
+            nomarchy.stateFile = ./theme-state.json;
+            home = {
+              inherit username;
+              homeDirectory = "/home/${username}";
+            };
+          }
+        ];
+      };
+    };
+}