Uploading the tool made on infinityfree to Play store legal?

Doing it in the frontend would solve the CPU usage on the server. But then it would be ever better to just bake the functionality right into the Android app and not wrap the website at all. It’s been a long time since I’ve touched any mobile development, but I’m pretty sure you can build cross platform apps with Javascript so you can reuse code and functionality between the website and app.