Participants were staying as 'non_member' after enrollment, causing
renewals to be priced at 900 (non-member) instead of 650 (member).
EnrollmentService now sets membership_type='member' on enrollment.

DB fix: updated 178 participants to 'member', corrected 124 unpaid
renewal invoices from 90000 to 65000 piasters.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>