POS Terminal now checks if an essential product was already purchased by
the selected participant this year. Shows amber warning with the purchase
date — allows the sale to proceed, just warns the admin.

Also expanded mobile app plan with: explore academy (news, gallery),
shop for essential products from app, event registration, and the
corresponding API endpoints needed on the system side.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>