- Add groupId field to ScheduleClass for admin-defined group identity - Add versioned DB migration system (replaces initTables) to prevent data loss - Redesign GroupView: Trainer → Class Type → Group → Datetimes hierarchy - Group datetimes by day, merge days with identical time sets - Auto-assign groupIds to legacy schedule entries in admin - Add mc_registrations CRUD to db.ts Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>