feat (backend): Add backend API to get flow info for subscriptions

backend/src/restful/index.js

@@ -66,6 +66,7 @@ function getEnv(req, res) {
     if (isLoon) backend = 'Loon';
     if (isSurge) backend = 'Surge';
     res.json({
+        status: 200,
         backend,
     });
 }