Answering my own question, to some extent:
The error I am getting is:
“EMPTY_CONTEXT_PATH”: “The context path is either empty or not defined.”,
This error is nothing to do with where static resources are loaded from and everything to do with the fact that there is no Process Application (see here)
Once a Process Application (not just a process engine) has been deployed, then and only then, is it possible to load custom forms.
And the html forms are indeed loaded from classpath://static/*
Many thanks for the help/pointers above