feat(expenses): add beloPrice and usdcEquivalent fields to Expense model and update related logic

apps/backend/prisma/migrations/20260608223915_add_belo_quote_to_expenses/migration.sql

@@ -0,0 +1,3 @@
+-- AlterTable
+ALTER TABLE "expenses" ADD COLUMN     "beloPrice" MONEY,
+ADD COLUMN     "usdcEquivalent" DECIMAL(12,6);

apps/backend/prisma/schema.prisma

@@ -130,6 +130,8 @@ model Expense {
   month             Int
   amount            Decimal          @db.Money
   amountPayed       Decimal?         @db.Money
+  beloPrice         Decimal?         @db.Money
+  usdcEquivalent    Decimal?         @db.Decimal(12, 6)
   status            PaymentStatus    @default(PENDING)
   dueDate           DateTime
   paymentDate       DateTime?