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/panels/speedtest/Panel.qml

@@ -149,7 +149,7 @@ Item {
       }
 
       if (!root.expectedStop && exitCode !== 0) {
-        root.error = root.stderrText || "Speed test failed"
+        root.error = root.stderrText || I18n.tr("Speed test failed")
         root.phase = ""
         root.running = false
         return
@@ -177,7 +177,7 @@ Item {
       onStreamFinished: {
         var fields = String(text || "").trim().split("\t")
         if (fields[0] === "wifi") root.connectionName = fields[1] || "Wi-Fi"
-        else if (fields[0] === "ethernet") root.connectionName = "Ethernet"
+        else if (fields[0] === "ethernet") root.connectionName = I18n.tr("Ethernet")
       }
     }
   }
@@ -186,9 +186,9 @@ Item {
     fontFamily: Style.font.family
     layerNamespace: "omarchy-network-speedtest"
     title: root.connectionName
-    leftLabel: "DOWNLOAD"
-    rightLabel: "UPLOAD"
-    runAgainTooltip: "Measure again via fast.com"
+    leftLabel: I18n.tr("DOWNLOAD")
+    rightLabel: I18n.tr("UPLOAD")
+    runAgainTooltip: I18n.tr("Measure again via fast.com")
     running: root.running
     leftValue: root.downloadValue
     rightValue: root.uploadValue