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/btop.nix

@@ -0,0 +1,61 @@
+# btop — themed from per-theme assets, baked at eval time.
+# A hand-made themes/<slug>/btop.theme asset wins; otherwise a theme is
+# generated from the palette, so custom themes get a themed btop too.
+{ config, lib, ... }:
+
+let
+  t = config.nomarchy.theme;
+  c = t.colors;
+
+  asset = config.nomarchy.themesDir + "/${t.slug}/btop.theme";
+
+  generated =
+    let
+      pairs = {
+        main_bg = c.base;
+        main_fg = c.text;
+        title = c.text;
+        hi_fg = c.accent;
+        selected_bg = c.overlay;
+        selected_fg = c.text;
+        inactive_fg = c.muted;
+        graph_text = c.subtext;
+        meter_bg = c.surface;
+        proc_misc = c.accentAlt;
+        cpu_box = c.accent;
+        mem_box = c.good;
+        net_box = c.accentAlt;
+        proc_box = c.surface;
+        div_line = c.overlay;
+        temp_start = c.good;
+        temp_mid = c.warn;
+        temp_end = c.bad;
+        cpu_start = c.good;
+        cpu_mid = c.warn;
+        cpu_end = c.bad;
+        free_start = c.good;
+        used_start = c.warn;
+        download_start = c.accent;
+        upload_start = c.accentAlt;
+      };
+    in
+    lib.concatStringsSep "\n"
+      (lib.mapAttrsToList (k: v: "theme[${k}]=\"${v}\"") pairs) + "\n";
+in
+{
+  config = lib.mkIf config.nomarchy.btop.enable {
+    programs.btop = {
+      enable = true;
+      settings = {
+        color_theme = "nomarchy";
+        theme_background = false; # let the terminal's opacity show through
+        vim_keys = true;
+      };
+    };
+
+    xdg.configFile."btop/themes/nomarchy.theme" =
+      if builtins.pathExists asset
+      then { source = asset; }
+      else { text = generated; };
+  };
+}