fix(client/notif): 通知占位示例文案改英文(默认语言一致,避免英文 app 显中文)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

client/lib/screens/notifications_page.dart

@@ -35,24 +35,24 @@ class NotificationsScreen extends ConsumerWidget {
         icon: PangolinIcons.bell,
         status: PangolinStatus.neutral,
         typeLabel: t.notifTypeNews,
-        title: '产品动态标题占位',
+        title: 'Product update', // TODO(spec-3): placeholder
-        sub: '2 天前',
+        sub: '2 days ago',
         read: false,
       ),
       (
         icon: PangolinIcons.zap,
         status: PangolinStatus.connected,
         typeLabel: t.notifTypeFeature,
-        title: '新功能上线标题占位',
+        title: 'New feature released', // TODO(spec-3): placeholder
-        sub: '5 天前',
+        sub: '5 days ago',
         read: false,
       ),
       (
         icon: PangolinIcons.alertTriangle,
         status: PangolinStatus.error,
         typeLabel: t.notifTypeImportant,
-        title: '重要通知标题占位',
+        title: 'Important notice', // TODO(spec-3): placeholder
-        sub: '1 周前',
+        sub: '1 week ago',
         read: true,
       ),
     ];