Introduces BalanceTransaction model to track per-user balance history
(prepayments, refunds, partner credits). Admin can add/delete transactions;
current balance is computed as the running sum.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
- Add phone/birthday columns via Prisma migration
- Admin user page shows phone and birthday with inline edit UI
- UserContactEditor client component for editing contact info
- updateUserContact server action with admin-only guard
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>