Split up the single prompt box into multiple fields

### What feature do you want to see added?

Instead of a single prompt box, consider using a form that asks for specific details of the prototype that the user wants to create.

### Why do you want this feature? Does it solve a problem?

Users are unsure what information they should put in the box, and a structured form might guide them to provide useful information to the LLM.

### How should the feature be implemented?

Consider asking for the form name, the audience, a list of form fields or questions, and any further context or instructions.

The user should be able to switch between the structured form and the single box (don't remove the current functionality).

Also consider that the help guide will need to be updated.

### Additional context (if applicable)

_No response_

Start by locating the current single prompt box and the help guide in the repository, then trace how prompt submissions reach prototype generation. Define the structured fields and switching behavior while preserving the existing single-box path, and update the help guide to describe both options.

Written by the indexing model from the issue text.