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>

modules/home/theme.nix

@@ -0,0 +1,69 @@
+# Nomarchy theming engine.
+#
+# nomarchy.stateFile (theme-state.json, inside the consuming flake) is
+# ingested at evaluation time — pure, because flake files are store
+# paths — and exposed to every other module as `config.nomarchy.theme`.
+#
+# Theme changes are fully Home Manager managed: `nomarchy-theme-sync
+# apply <theme>` writes the JSON and runs `home-manager switch`, baking
+# everything (Hyprland, Waybar, Ghostty, btop, Stylix) into one
+# read-only generation. No runtime patching, no partial states; theme
+# history is generation history.
+#
+# The one runtime exception is the wallpaper (swww is imperative by
+# nature): applied at session start, after every switch (hook below),
+# and cycled instantly with `nomarchy-theme-sync bg next`.
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.nomarchy;
+
+  themeState = builtins.fromJSON (builtins.readFile cfg.stateFile);
+
+  # Defaults guarantee evaluation succeeds on a sparse or older state
+  # file (e.g. one written before a schema field was added). The shipped
+  # Tokyo Night preset provides the color/ansi fallbacks; the path is
+  # relative to this module, so it resolves inside Nomarchy's own flake
+  # source even when consumed downstream.
+  preset = builtins.fromJSON (builtins.readFile ../../themes/tokyo-night.json);
+
+  defaults = preset // {
+    fonts = {
+      mono = "JetBrainsMono Nerd Font";
+      ui = "Inter";
+      size = 11;
+    };
+    ui = {
+      gapsIn = 5;
+      gapsOut = 12;
+      borderSize = 2;
+      rounding = 10;
+      activeOpacity = 1.0;
+      inactiveOpacity = 0.95;
+      terminalOpacity = 0.96;
+      blur = true;
+      shadow = true;
+    };
+  };
+in
+{
+  config = {
+    nomarchy.theme = lib.recursiveUpdate defaults themeState;
+
+    nomarchy.lib = {
+      # "#7aa2f7" -> "rgb(7aa2f7)"          (Hyprland color syntax)
+      rgb = c: "rgb(${lib.removePrefix "#" c})";
+      # "#16161e" -> "rgba(16161eaa)"       (Hyprland color + hex alpha)
+      rgba = c: alpha: "rgba(${lib.removePrefix "#" c}${alpha})";
+    };
+
+    home.packages = [ cfg.package ];
+
+    # After a switch the new theme's wallpaper should show without
+    # logging out. Best-effort: outside a graphical session swww isn't
+    # running and this is a no-op.
+    home.activation.nomarchyWallpaper = lib.hm.dag.entryAfter [ "writeBoundary" ] ''
+      run ${lib.getExe cfg.package} --quiet wallpaper || true
+    '';
+  };
+}