New wizard at /receptionist/retroactive-enrollment lets staff enroll
participants who started in previous months. Flow: select participant →
choose program → set actual start date → mark each month as unpaid or
paid-outside-system → optionally pay all outstanding now. Creates
individual invoices per month with proper metadata. Supports admin price
override for the total. Accessible from receptionist dashboard with
enrollments.create permission.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>