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.

shell/Ui/SearchableDropdown.qml

@@ -22,8 +22,8 @@ Item {
   property string label: ""
   property string value: ""
   property var options: []
-  property string placeholderText: "Search..."
-  property string emptyText: "No matches"
+  property string placeholderText: I18n.tr("Search...")
+  property string emptyText: I18n.tr("No matches")
   property string triggerLabel: ""
 
   property color foreground: Commons.Color.popups.text