feat(#37): módulo de cartão de crédito com faturas mensais

- Migration 011: closing_day/due_day em accounts + tabela credit_bills
- CreditBillService: cria/atualiza fatura corrente on-demand no GET /accounts
- Widget FATURA ATUAL no dashboard com total e botão PAGAR
- AccountsView: campos closing_day/due_day para contas credit + painel fatura
- Dashboard: current_bills lista faturas não pagas de todos os cartões

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

apps/api/internal/service/credit_bill.go

@@ -0,0 +1,95 @@
+package service
+
+import (
+	"context"
+	"errors"
+	"time"
+
+	"financeiro-carvalho/internal/model"
+	"financeiro-carvalho/internal/repository"
+)
+
+var ErrBillNotCreditAccount = errors.New("account is not a credit card account")
+
+type CreditBillService struct {
+	repo        repository.CreditBillRepository
+	accountRepo repository.AccountRepoWithYield
+}
+
+func NewCreditBillService(repo repository.CreditBillRepository, accountRepo repository.AccountRepoWithYield) *CreditBillService {
+	return &CreditBillService{repo: repo, accountRepo: accountRepo}
+}
+
+func (s *CreditBillService) ListByAccount(ctx context.Context, accountID int) ([]model.CreditBill, error) {
+	bills, err := s.repo.ListByAccount(ctx, accountID)
+	if bills == nil {
+		return []model.CreditBill{}, err
+	}
+	return bills, err
+}
+
+func (s *CreditBillService) GetCurrent(ctx context.Context, accountID int) (*model.CreditBill, error) {
+	return s.repo.GetCurrent(ctx, accountID)
+}
+
+// EnsureCurrentBill creates (or refreshes) the current open bill for a credit account
+// using the account's closing_day and due_day config (defaults: closing=1, due=10).
+func (s *CreditBillService) EnsureCurrentBill(ctx context.Context, accountID int, closingDay, dueDay int) error {
+	if closingDay == 0 {
+		closingDay = 1
+	}
+	if dueDay == 0 {
+		dueDay = 10
+	}
+
+	now := time.Now()
+	// Determine the current billing period based on closing day
+	var periodStart, periodEnd time.Time
+	if now.Day() > closingDay {
+		// We're after the closing day: current period is from closingDay+1 this month to closingDay next month
+		y, m, _ := now.Date()
+		periodStart = time.Date(y, m, closingDay+1, 0, 0, 0, 0, time.UTC)
+		next := time.Date(y, m+1, closingDay, 0, 0, 0, 0, time.UTC)
+		periodEnd = next
+	} else {
+		// We're before the closing day: current period is from closingDay+1 last month to closingDay this month
+		y, m, _ := now.Date()
+		periodStart = time.Date(y, m-1, closingDay+1, 0, 0, 0, 0, time.UTC)
+		periodEnd = time.Date(y, m, closingDay, 0, 0, 0, 0, time.UTC)
+	}
+	// Due date: dueDay of the month after periodEnd
+	dueDate := time.Date(periodEnd.Year(), periodEnd.Month()+1, dueDay, 0, 0, 0, 0, time.UTC)
+
+	in := model.CreditBillInput{
+		AccountID:   accountID,
+		PeriodStart: periodStart.Format("2006-01-02"),
+		PeriodEnd:   periodEnd.Format("2006-01-02"),
+		DueDate:     dueDate.Format("2006-01-02"),
+	}
+	_, err := s.repo.Upsert(ctx, in)
+	return err
+}
+
+func (s *CreditBillService) MarkPaid(ctx context.Context, id int, paymentAccountID *int) error {
+	return s.repo.MarkPaid(ctx, id, paymentAccountID)
+}
+
+// currentBillsForDashboard returns unpaid current bills across all credit accounts.
+func (s *CreditBillService) currentBillsForDashboard(ctx context.Context) ([]model.CreditBill, error) {
+	accounts, err := s.accountRepo.List(ctx)
+	if err != nil {
+		return nil, err
+	}
+	var bills []model.CreditBill
+	for _, a := range accounts {
+		if a.Type != "credit" {
+			continue
+		}
+		bill, err := s.repo.GetCurrent(ctx, a.ID)
+		if err != nil || bill == nil {
+			continue
+		}
+		bills = append(bills, *bill)
+	}
+	return bills, nil
+}