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/plugins/notifications/Service.qml

@@ -725,7 +725,7 @@ Item {
         originalId: -1,
         app: "omarchy-action",
         appIcon: "",
-        summary: "No recent notifications",
+        summary: I18n.tr("No recent notifications"),
         body: "",
         image: "",
         glyph: "󰂚",