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/model/account.go

@@ -8,6 +8,9 @@ type Account struct {
 	Balance        float64 `json:"balance"`
 	YieldType      string  `json:"yield_type"` // "none" | "cdi" | "variable"
 	LastYieldDate  *string `json:"last_yield_date,omitempty"`
+	ClosingDay     *int    `json:"closing_day,omitempty"`
+	DueDay         *int    `json:"due_day,omitempty"`
+	CurrentBill    *CreditBill `json:"current_bill,omitempty"`
 	CreatedAt      string  `json:"created_at"`
 	UpdatedAt      string  `json:"updated_at"`
 }
@@ -17,4 +20,6 @@ type AccountInput struct {
 	Type           string  `json:"type"`
 	InitialBalance float64 `json:"initial_balance"`
 	YieldType      string  `json:"yield_type"` // "none" | "cdi" | "variable"
+	ClosingDay     *int    `json:"closing_day,omitempty"`
+	DueDay         *int    `json:"due_day,omitempty"`
 }