AI question suggestions

Press AI question on any section to open a dialog that suggests a structured question block. It uses the same Turnstile-verified Worker as the text suggester, just in a different mode. The flow:

1. Pick a question type (the same eight types as the Add question menu).
2. The section title is used as the subject; the section's existing text is sent as context so the question is answerable from the lesson.
3. Turnstile verifies the request, then the verified token, subject, type, and context are POSTed to the Worker with mode: "question".
4. The Worker asks the model for JSON matching that question type (prompt, options, answer, etc.) and returns it.
5. The suggestion is inserted as a new, fully editable question block of that type, with option indexes mapped back onto option ids in packages/core/src/questions.js.

Every type in the Add question menu has an entry in QUESTION_SCHEMAS, QUESTION_LABELS and QUESTION_INSTRUCTIONS (apps/api/src/lib/ai/schemas.js); the Worker refuses a questionType it has no schema for with a 400, so a type in the menu without one is a button that only returns an error. Add all three entries whenever a question type is added.