Adds a "+ Доступ" button to each user row in the admin users table.
Clicking it opens a centered modal with a course dropdown, optional
expiry date, and a Server Action that upserts CourseEnrollment, logs
to AccessLog, and sends sendCourseAccessEmail on new enrollments.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
