overwritten changes in playground from previous tab 🤦

I know the playground isn't meant to be a place for serious apps, but I just overwritten my code because I had an older tab open and saved that one instead of the newer one. Three quality of life changes for the playground:

1. Some kind of safe-guards in place to prevent this older version of the code from saving would be cool.
2. Navigate away warning would be a good to have, you can easily make changes then click "fullscreen" and your changes don't save.
3. Auto detect JSX, was trying for 10 minutes to fix a bug and was because I didn't switch to jsx at the top dropdown.