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/Commons/I18n.qml

@@ -0,0 +1,16 @@
+pragma Singleton
+import QtQuick
+import "Tr.js" as Tr
+
+// tr("English %1", arg) returns the Chinese entry under zh_CN; plain JS imports Tr.js for the same.
+QtObject {
+  readonly property bool chinese: Tr.chinese
+
+  function tr() {
+    return Tr.tr.apply(null, arguments)
+  }
+
+  function trMatch(text, templates) {
+    return Tr.trMatch(text, templates)
+  }
+}