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/ConfirmDialog.qml

@@ -7,8 +7,8 @@ Item {
 
   property bool opened: false
   property string message: ""
-  property string cancelText: "Cancel"
-  property string confirmText: "Confirm"
+  property string cancelText: I18n.tr("Cancel")
+  property string confirmText: I18n.tr("Confirm")
   property int selectedIndex: 1
   property color background: Commons.Color.background
   property color foreground: Commons.Color.foreground

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

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

shell/Ui/SpeedTestOverlay.qml

@@ -23,7 +23,7 @@ PanelWindow {
   property string unit: "Mbps"
   property string title: ""
   property string layerNamespace: "omarchy-speed-test"
-  property string runAgainTooltip: "Measure again"
+  property string runAgainTooltip: I18n.tr("Measure again")
   property real leftValue: 0
   property real rightValue: 0
   property bool leftLive: false
@@ -165,7 +165,7 @@ PanelWindow {
         // Centered on the dial pair. Fades rather than unmounts while a run
         // is in flight, so the cluster never shifts.
         Button {
-          text: "Run Again"
+          text: I18n.tr("Run Again")
           tooltipText: root.runAgainTooltip
           bordered: true
           enabled: !root.running