Generate the structure configuration alongside the classes

Problem/Motivation

A generated class declares a structure id; the structure itself is configuration. If the two are produced by different runs or land in different places, a site ends up with a class pointing at a structure that does not exist — a 500 on an endpoint that looked fine in review.

Proposed resolution

• Emit the structure and endpoint entities in the same run as the classes, into the site's configuration.
• Respect what a person already changed: a property whose shape or key was set by hand is not reset to the default on the next run — editing the structure is the cheapest sanctioned way to change a response.
• Record on each generated property whether it came from the generator or from a person, which is what makes the previous point possible.
• The pair is atomic: classes and configuration land together or not at all.

Remaining tasks

Everything.