feat(settings): add enableLocalProxy toggle to gate main page proxy UI

New users often accidentally trigger ProxyToggle/FailoverToggle on the
main page. Add a settings toggle (default off) so the proxy controls
only appear when explicitly enabled. The proxy service start/stop in
settings remains independent of this visibility flag.

src/i18n/locales/en.json

@@ -192,6 +192,8 @@
       "proxy": {
         "title": "Local Proxy",
         "description": "Control proxy service toggle, view status and port info",
+        "enableFeature": "Show Proxy Toggle on Main Page",
+        "enableFeatureDescription": "When enabled, the proxy and failover toggles will appear at the top of the main page",
         "running": "Running",
         "stopped": "Stopped"
       },

src/i18n/locales/ja.json

@@ -192,6 +192,8 @@
       "proxy": {
         "title": "ローカルプロキシ",
         "description": "プロキシサービスの切り替え、ステータスとポート情報を表示",
+        "enableFeature": "メインページにプロキシ切り替えを表示",
+        "enableFeatureDescription": "有効にすると、メインページ上部にプロキシとフェイルオーバーの切り替えが表示されます",
         "running": "実行中",
         "stopped": "停止中"
       },

src/i18n/locales/zh.json

@@ -192,6 +192,8 @@
       "proxy": {
         "title": "本地代理",
         "description": "控制代理服务开关、查看状态与端口信息",
+        "enableFeature": "在主页面显示本地代理开关",
+        "enableFeatureDescription": "开启后，主页面顶部将显示代理和故障转移开关",
         "running": "运行中",
         "stopped": "已停止"
       },