Build an AI worksheet generator for teachers with these features:
1. An input form: subject, topic, grade level, question types (multiple choice, fill in the blank, short answer, matching), and difficulty level.
2. AI generates 10 to 20 questions with a full answer key and one-line explanations.
3. Three difficulty tiers auto-generated from a single prompt: below level, on level, and challenge.
4. A clean print layout: header with student name and date lines, numbered questions, and the answer key on a separate page.
5. A question bank builder so teachers can save, tag, and remix favorite questions across years.
6. A standards tagging field where teachers note curriculum codes, with a reminder to verify alignment.
7. An editable question list with a regenerate-this-question button per item.
8. Export to PDF plus a Google Docs-friendly format.
9. A quick preview modal that shows exactly how the printed page will look.