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/retro-82.json

@@ -0,0 +1,39 @@
+{
+  "version": 1,
+  "name": "Retro 82",
+  "slug": "retro-82",
+  "mode": "dark",
+  "wallpaper": "",
+  "colors": {
+    "base": "#05182e",
+    "mantle": "#041427",
+    "surface": "#00172e",
+    "overlay": "#134e5a",
+    "text": "#f6dcac",
+    "subtext": "#a7c9c6",
+    "muted": "#134e5a",
+    "accent": "#faa968",
+    "accentAlt": "#3f8f8a",
+    "good": "#028391",
+    "warn": "#e97b3c",
+    "bad": "#f85525"
+  },
+  "ansi": [
+    "#00172e",
+    "#f85525",
+    "#028391",
+    "#e97b3c",
+    "#faa968",
+    "#3f8f8a",
+    "#8cbfb8",
+    "#a7c9c6",
+    "#134e5a",
+    "#f85525",
+    "#028391",
+    "#e97b3c",
+    "#faa968",
+    "#3f8f8a",
+    "#8cbfb8",
+    "#f6dcac"
+  ]
+}