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/MultiSelect.qml

@@ -28,9 +28,9 @@ Item {
   property var options: []
   property var optionsCommand: []
   property string optionsCommandCwd: ""
-  property string placeholderText: "Search..."
-  property string emptyText: "No options"
-  property string noSelectionText: "None selected"
+  property string placeholderText: I18n.tr("Search...")
+  property string emptyText: I18n.tr("No options")
+  property string noSelectionText: I18n.tr("None selected")
   property string triggerLabel: ""
   property bool showLabel: true
 
@@ -493,7 +493,7 @@ Item {
               textFormat: Text.PlainText
               anchors.centerIn: parent
               visible: resultList.count === 0
-              text: root.loadingOptions ? "Loading…" : (root.optionsError !== "" ? root.optionsError : root.emptyText)
+              text: root.loadingOptions ? I18n.tr("Loading…") : (root.optionsError !== "" ? root.optionsError : root.emptyText)
               color: Qt.darker(root.foreground, 1.6)
               font.family: root.fontFamily
               font.pixelSize: Style.font.body