Add Simplified Chinese as a system language

The installer asks for the language before the keyboard, and
Setup > Language (omarchy language en|zh) switches it later. Under
zh_CN the menu reads its labels from omarchy-menu.zh-cn.jsonc, the
shell from I18nZh.js through I18n.tr, and notifications are worded
by their sender through omarchy-text, which reads the same table.
User text is never translated.

bin/omarchy-theme-bg-next

@@ -17,7 +17,7 @@ mapfile -d '' -t BACKGROUNDS < <(
 TOTAL=${#BACKGROUNDS[@]}
 
 if (( TOTAL == 0 )); then
-  omarchy-notification-send "No background was found for theme" -t 2000
+  omarchy-notification-send "$(omarchy-text "No background was found for theme")" -t 2000
 else
   # Get current background from symlink
   if [[ -L $CURRENT_BACKGROUND_LINK ]]; then