Design a learning management system (LMS) with courses, enrollments, and progress tracking.

users(id, role CHECK IN ('student','instructor','admin'), email UNIQUE, name) courses(id, title, instructor_id FK, status, price DECIMAL, created_at) lessons(id, course_id FK, title, content, order_position INT, duration_seconds INT, UNIQUE(course_id, order_position)) enrollments(student_id FK, course_id FK, enrolled_at, completed_at NULLABLE, progress_pct DECIMAL(5,2), PRIMARY KEY(student_id, cou