new app does not appear in banglejs.com/apps

Do I have to specify this somewhere which files are uploaded?

Yes - that's what goes in the storage entry for the app in apps.json. You can't upload the png images directly - you need to have converted them to binary. Easiest method is just to use the Web IDE to take the existing image files off your watch and save them to files.

I think given the image is for the entire background it's better to leave it as a file rather than loading it in the source. For smaller images I'd say definitely just stick them in the JS though