Add Omarchy-style Hyprland desktop for straylight

Ports the classic dotfiles Omarchy setup to a no-home-manager NixOS
system module (configs/omarchy.nix), scoped to straylight only so the
other desktop hosts keep i3.

- Hyprland (programs.hyprland) becomes the default lightdm session; i3
  stays enabled and selectable as a fallback.
- Omarchy config layout under ~/.config/{hypr,waybar,rofi,wlogout,
  swayosd,alacritty} symlinked from the store; mutable theme/wallpaper
  state in ~/.config/omarchy/current.
- omarchy-dots generates 8 themes (hyprland/hyprlock/waybar/rofi/
  swayosd/wlogout/alacritty/mako colour files) from each theme's
  palette, with wallpapers fetched from the Omarchy v3.8.4 tag.
- Helper scripts: omarchy-theme-set/bg-next/bg-set/apply, omarchy-menu
  (rofi power/theme/background menus), waybar toggle, screenshot, lock.
- Shared desktop modules (desktop.nix / desktop-light.nix) untouched.

configs/omarchy/bin/omarchy-menu

@@ -0,0 +1,62 @@
+#!/usr/bin/env bash
+# rofi-based Omarchy menu. Replaces Omarchy v3's walker-driven omarchy-menu.
+# Usage: omarchy-menu [system|theme|background|capture|keybindings]
+set -euo pipefail
+
+OMARCHY_PATH="${OMARCHY_PATH:-$HOME/.local/share/omarchy}"
+CURRENT="$HOME/.config/omarchy/current"
+PICK=(rofi -dmenu -i -p "" -theme-str 'window { width: 22%; } listview { lines: 8; }')
+
+menu_main() {
+  local choice
+  choice="$(printf '%s\n' Apps Themes Backgrounds Capture System Keybindings | "${PICK[@]}")" || exit 0
+  case "$choice" in
+    Apps) rofi -show drun -show-icons ;;
+    Themes) menu_theme ;;
+    Backgrounds) omarchy-theme-bg-next ;;
+    Capture) menu_capture ;;
+    System) menu_system ;;
+    Keybindings) menu_keybindings ;;
+  esac
+}
+
+menu_system() {
+  local choice
+  choice="$(printf '%s\n' Lock Logout Suspend Reboot Shutdown | "${PICK[@]}")" || exit 0
+  case "$choice" in
+    Lock) omarchy-system-lock ;;
+    Logout) hyprctl dispatch exit ;;
+    Suspend) systemctl suspend ;;
+    Reboot) systemctl reboot ;;
+    Shutdown) systemctl poweroff ;;
+  esac
+}
+
+menu_theme() {
+  local choice
+  choice="$(find "$OMARCHY_PATH/themes" -maxdepth 1 -mindepth 1 -type d -printf '%f\n' | sort | "${PICK[@]}")" || exit 0
+  [ -n "$choice" ] && omarchy-theme-set "$choice"
+}
+
+menu_capture() {
+  local choice
+  choice="$(printf '%s\n' Region Window Output | "${PICK[@]}")" || exit 0
+  case "$choice" in
+    Region) omarchy-capture-screenshot region ;;
+    Window) omarchy-capture-screenshot window ;;
+    Output) omarchy-capture-screenshot output ;;
+  esac
+}
+
+menu_keybindings() {
+  alacritty -e less ~/.config/hypr/bindings.conf
+}
+
+case "${1:-}" in
+  system) menu_system ;;
+  theme) menu_theme ;;
+  background) omarchy-theme-bg-next ;;
+  capture) menu_capture ;;
+  keybindings) menu_keybindings ;;
+  "" | *) menu_main ;;
+esac