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/summer-night.json

@@ -0,0 +1,39 @@
+{
+  "version": 1,
+  "name": "Summer Night",
+  "slug": "summer-night",
+  "mode": "dark",
+  "wallpaper": "",
+  "colors": {
+    "base": "#2d353b",
+    "mantle": "#262d32",
+    "surface": "#3c474d",
+    "overlay": "#868d80",
+    "text": "#d3c6aa",
+    "subtext": "#868d80",
+    "muted": "#868d80",
+    "accent": "#83b6af",
+    "accentAlt": "#d39bb6",
+    "good": "#a7c080",
+    "warn": "#d9bb80",
+    "bad": "#e68183"
+  },
+  "ansi": [
+    "#3c474d",
+    "#e68183",
+    "#a7c080",
+    "#d9bb80",
+    "#83b6af",
+    "#d39bb6",
+    "#87c095",
+    "#868d80",
+    "#868d80",
+    "#e68183",
+    "#a7c080",
+    "#d9bb80",
+    "#83b6af",
+    "#d39bb6",
+    "#87c095",
+    "#868d80"
+  ]
+}