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>

themes/ethereal.json

@@ -0,0 +1,39 @@
+{
+  "version": 1,
+  "name": "Ethereal",
+  "slug": "ethereal",
+  "mode": "dark",
+  "wallpaper": "",
+  "colors": {
+    "base": "#060B1E",
+    "mantle": "#05091a",
+    "surface": "#060B1E",
+    "overlay": "#6d7db6",
+    "text": "#ffcead",
+    "subtext": "#F99957",
+    "muted": "#6d7db6",
+    "accent": "#7d82d9",
+    "accentAlt": "#c89dc1",
+    "good": "#92a593",
+    "warn": "#E9BB4F",
+    "bad": "#ED5B5A"
+  },
+  "ansi": [
+    "#060B1E",
+    "#ED5B5A",
+    "#92a593",
+    "#E9BB4F",
+    "#7d82d9",
+    "#c89dc1",
+    "#a3bfd1",
+    "#F99957",
+    "#6d7db6",
+    "#faaaa9",
+    "#c4cfc4",
+    "#f7dc9c",
+    "#c2c4f0",
+    "#ead7e7",
+    "#dfeaf0",
+    "#ffcead"
+  ]
+}