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>

tools/import-palettes.py

@@ -0,0 +1,96 @@
+#!/usr/bin/env python3
+"""Convert old-distro palettes (colors.toml) into Nomarchy theme JSON presets.
+
+Usage:  tools/import-palettes.py <old-palettes-dir> <output-themes-dir>
+
+Old format (per theme directory):
+    colors.toml     kitty-style keys: background, foreground, accent,
+                    selection_background, color0..color15
+    light.mode      marker file: theme is light
+    icons.theme     icon theme name (informational, ignored for now)
+    backgrounds/    wallpapers
+    apps/           hand-made per-app theme files (btop.theme, ...)
+
+Output, per theme:
+    <slug>.json            the palette (Nomarchy theme schema)
+    <slug>/backgrounds/    wallpapers, copied verbatim
+    <slug>/btop.theme      copied from apps/ when present
+"""
+
+import json
+import shutil
+import sys
+import tomllib
+from pathlib import Path
+
+
+def darken(hex_color: str, factor: float = 0.85) -> str:
+    """Scale a #rrggbb color toward black (used to derive 'mantle')."""
+    h = hex_color.lstrip("#")
+    r, g, b = (int(h[i:i + 2], 16) for i in (0, 2, 4))
+    return "#{:02x}{:02x}{:02x}".format(*(round(v * factor) for v in (r, g, b)))
+
+
+def convert(theme_dir: Path) -> dict:
+    toml = tomllib.loads((theme_dir / "colors.toml").read_text())
+    slug = theme_dir.name
+    ansi = [toml[f"color{i}"] for i in range(16)]
+
+    return {
+        "version": 1,
+        "name": slug.replace("-", " ").title(),
+        "slug": slug,
+        "mode": "light" if (theme_dir / "light.mode").exists() else "dark",
+        # Empty = auto: nomarchy-theme-sync falls back to the first file in
+        # the theme's backgrounds/ directory.
+        "wallpaper": "",
+        "colors": {
+            "base": toml["background"],
+            "mantle": darken(toml["background"]),
+            "surface": toml["color0"],
+            "overlay": toml["color8"],
+            "text": toml["foreground"],
+            "subtext": toml["color7"],
+            "muted": toml["color8"],
+            "accent": toml["accent"],
+            "accentAlt": toml["color5"],
+            "good": toml["color2"],
+            "warn": toml["color3"],
+            "bad": toml["color1"],
+        },
+        "ansi": ansi,
+    }
+
+
+def main() -> None:
+    if len(sys.argv) != 3:
+        sys.exit(__doc__)
+    src, out = Path(sys.argv[1]), Path(sys.argv[2])
+    out.mkdir(parents=True, exist_ok=True)
+
+    converted = 0
+    for theme_dir in sorted(src.iterdir()):
+        if not (theme_dir / "colors.toml").is_file():
+            continue
+        theme = convert(theme_dir)
+        slug = theme["slug"]
+        (out / f"{slug}.json").write_text(json.dumps(theme, indent=2) + "\n")
+
+        # Assets: wallpapers and hand-made per-app theme files.
+        extras = []
+        if (theme_dir / "backgrounds").is_dir():
+            shutil.copytree(theme_dir / "backgrounds", out / slug / "backgrounds",
+                            dirs_exist_ok=True)
+            extras.append(f"{len(list((theme_dir / 'backgrounds').iterdir()))} wallpapers")
+        if (theme_dir / "apps" / "btop.theme").is_file():
+            (out / slug).mkdir(parents=True, exist_ok=True)
+            shutil.copyfile(theme_dir / "apps" / "btop.theme", out / slug / "btop.theme")
+            extras.append("btop")
+
+        print(f"  {slug:<20} ({theme['mode']}{', ' + ', '.join(extras) if extras else ''})")
+        converted += 1
+    print(f"converted {converted} palettes -> {out}")
+
+
+if __name__ == "__main__":
+    main()