Self-service "pay now" flows (registration success + user dashboard) now go
straight to a Yoco checkout for the full outstanding balance instead of
prompting for a partial amount; that page has been removed. Partial-amount
payment links remain supervisor/admin-only via the Payments dashboard.
Also adds a "Record Payment" tab to the supervisor manual registration page,
pre-filled with the most recently created registration, so staff can capture
a payment right after registering someone without leaving the page.
joshua