Allow generating a full Shiny app (ie. an actual "app.R" file) that just hosts a form

The main use of the package is to provide Shiny modules (but users don't need to know that, it abstracts that complexity away from them) so that a form can be plugged into any Shiny app. But it could be nice for people who want to make the form an entire standalone app to let them do that (a couple women from runconf16 told me they'd love that)

Start by locating the package entry point that currently creates a form or Shiny module; the issue names the desired standalone app.R output but no existing file or test. Confirm how a generated app.R would launch as a Shiny app and host only the form, then add coverage showing that the standalone app runs and renders the form.

Written by the indexing model from the issue text.