feat: add Copayment and Adjustment columns to payments table

- Added copayment and adjustment fields (Decimal, default 0) to Payment
  model in schema and directly to DB via ALTER TABLE
- Added PATCH /api/payments/:id/copayment and /adjustment routes
- Added inline-editable Copayment and Adjustment columns after MH Paid
  with same click-to-edit format; Copayment in blue, Adjustment in orange

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/db/prisma/schema.prisma

@@ -331,6 +331,8 @@ model Payment {
   totalAdjusted Decimal       @default(0.00) @db.Decimal(10, 2)
   totalDue      Decimal       @db.Decimal(10, 2)
   mhPaidAmount  Decimal?      @db.Decimal(10, 2)
+  copayment     Decimal       @default(0.00) @db.Decimal(10, 2)
+  adjustment    Decimal       @default(0.00) @db.Decimal(10, 2)
   status        PaymentStatus @default(PENDING)
   notes         String?
   icn           String?