mathconceicion/study_flow ? reverse-engineered prompt

Build me a Flutter app for studying for the ENEM that feels simple and easy to use.

I want a home screen with the main subject areas, and when I tap one, it should open a page with the study topics for that subject. Let me filter the topics by difficulty, like all, basic, intermediate, and advanced. Each topic should open its own details page.

Also add a section for real ENEM questions pulled from a public API at runtime, with loading states and a friendly error message if something goes wrong. When I open a question, I want to see the full statement, any images, the answer choices, and the correct answer after checking it.

Use the local study data for the subjects and topics, and make the app work cleanly on mobile, web, and desktop if possible. If you need to look up current docs online, feel free to do that.