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/hypr/envs.conf

@@ -0,0 +1,27 @@
+# Environment for Hyprland sessions (Omarchy v3 default/hypr/envs.conf).
+# GUM env source dropped (not installed); XCOMPOSEFILE dropped (no ~/.XCompose).
+
+# Cursor size
+env = XCURSOR_SIZE,24
+env = HYPRCURSOR_SIZE,24
+
+# Force all apps to use Wayland
+env = GDK_BACKEND,wayland,x11,*
+env = QT_QPA_PLATFORM,wayland;xcb
+env = MOZ_ENABLE_WAYLAND,1
+env = ELECTRON_OZONE_PLATFORM_HINT,wayland
+env = OZONE_PLATFORM,wayland
+env = XDG_SESSION_TYPE,wayland
+
+# Allow better support for screen sharing (Google Meet, Discord, etc)
+env = XDG_CURRENT_DESKTOP,Hyprland
+env = XDG_SESSION_DESKTOP,Hyprland
+
+xwayland {
+  force_zero_scaling = true
+}
+
+# Don't show update on first launch
+ecosystem {
+  no_update_news = true
+}