Add PDF_ATTACHMENT stimulus kind and MinIO pdf upload (media_type=pdf) for question-side PDFs.
Reject top-level question_text on DYNAMIC create/update; omit it from API responses and derive stored text from stimulus only.
Expand DYNAMIC_QUESTION_TYPE_BUILDER_ADMIN_INTEGRATION.md with full API request/response reference and workflows.
Co-authored-by: Cursor <cursoragent@cursor.com>
