Function save_research_form 

pub async fn save_research_form(
    conn: &mut PgConnection,
    course_id: Uuid,
    content: Value,
) -> ModelResult<ResearchForm>

Saves a course’s research consent form and makes its question rows match the question blocks in content: questions whose block was removed are soft-deleted.

Errors with InvalidRequest if the content has no questions, a question is empty, or a question id belongs to another course.