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/ristretto.json

@@ -0,0 +1,39 @@
+{
+  "version": 1,
+  "name": "Ristretto",
+  "slug": "ristretto",
+  "mode": "dark",
+  "wallpaper": "",
+  "colors": {
+    "base": "#2c2525",
+    "mantle": "#251f1f",
+    "surface": "#72696a",
+    "overlay": "#948a8b",
+    "text": "#e6d9db",
+    "subtext": "#e6d9db",
+    "muted": "#948a8b",
+    "accent": "#f38d70",
+    "accentAlt": "#a8a9eb",
+    "good": "#adda78",
+    "warn": "#f9cc6c",
+    "bad": "#fd6883"
+  },
+  "ansi": [
+    "#72696a",
+    "#fd6883",
+    "#adda78",
+    "#f9cc6c",
+    "#f38d70",
+    "#a8a9eb",
+    "#85dacc",
+    "#e6d9db",
+    "#948a8b",
+    "#ff8297",
+    "#c8e292",
+    "#fcd675",
+    "#f8a788",
+    "#bebffd",
+    "#9bf1e1",
+    "#f1e5e7"
+  ]
+}