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>

pkgs/nomarchy-theme-sync/default.nix

@@ -0,0 +1,49 @@
+{ lib
+, stdenvNoCC
+, python3
+, makeWrapper
+, swww
+, libnotify
+, git
+  # Shipped theme presets, baked into the package as a fallback so
+  # `list`/`apply` work even when $NOMARCHY_PATH has no themes/ dir.
+, themesDir ? null
+}:
+
+stdenvNoCC.mkDerivation {
+  pname = "nomarchy-theme-sync";
+  version = "0.4.0";
+
+  src = ./.;
+
+  nativeBuildInputs = [ makeWrapper ];
+  buildInputs = [ python3 ];
+
+  installPhase = ''
+    runHook preInstall
+
+    install -Dm755 nomarchy-theme-sync.py $out/bin/nomarchy-theme-sync
+    patchShebangs $out/bin/nomarchy-theme-sync
+
+    ${lib.optionalString (themesDir != null) ''
+      mkdir -p $out/share/nomarchy
+      cp -r ${themesDir} $out/share/nomarchy/themes
+    ''}
+
+    # Stdlib-only Python. home-manager is deliberately NOT wrapped in —
+    # the rebuild must use the user's own home-manager from their PATH.
+    wrapProgram $out/bin/nomarchy-theme-sync \
+      --prefix PATH : ${lib.makeBinPath [ swww libnotify git ]} \
+      ${lib.optionalString (themesDir != null)
+        "--set NOMARCHY_DEFAULT_THEMES $out/share/nomarchy/themes"}
+
+    runHook postInstall
+  '';
+
+  meta = {
+    description = "Nomarchy theming: JSON state writer + Home Manager rebuild dispatcher";
+    license = lib.licenses.mit;
+    mainProgram = "nomarchy-theme-sync";
+    platforms = lib.platforms.linux;
+  };
+}