feat(#21): contas bancárias e patrimônio consolidado

CRUD de contas (corrente/poupança/investimento/cartão) com saldo calculado
automaticamente. account_id nullable em transactions. Widget patrimônio no
dashboard. Tela /contas. Seletor de conta nas transações manuais.

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

apps/api/internal/service/account.go

@@ -0,0 +1,70 @@
+package service
+
+import (
+	"context"
+	"errors"
+
+	"financeiro-carvalho/internal/model"
+)
+
+var (
+	ErrAccountEmptyName   = errors.New("account name cannot be empty")
+	ErrAccountInvalidType = errors.New("account type must be checking, savings, investment, or credit")
+)
+
+var validAccountTypes = map[string]bool{
+	"checking": true, "savings": true, "investment": true, "credit": true,
+}
+
+type AccountRepo interface {
+	List(ctx context.Context) ([]model.Account, error)
+	GetByID(ctx context.Context, id int) (*model.Account, error)
+	Create(ctx context.Context, in model.AccountInput) (*model.Account, error)
+	Update(ctx context.Context, id int, in model.AccountInput) (*model.Account, error)
+	Delete(ctx context.Context, id int) error
+	TotalPatrimony(ctx context.Context) (float64, error)
+}
+
+type AccountService struct {
+	repo AccountRepo
+}
+
+func NewAccountService(repo AccountRepo) *AccountService {
+	return &AccountService{repo: repo}
+}
+
+func (s *AccountService) validate(in model.AccountInput) error {
+	if in.Name == "" {
+		return ErrAccountEmptyName
+	}
+	if !validAccountTypes[in.Type] {
+		return ErrAccountInvalidType
+	}
+	return nil
+}
+
+func (s *AccountService) List(ctx context.Context) ([]model.Account, error) {
+	return s.repo.List(ctx)
+}
+
+func (s *AccountService) Create(ctx context.Context, in model.AccountInput) (*model.Account, error) {
+	if err := s.validate(in); err != nil {
+		return nil, err
+	}
+	return s.repo.Create(ctx, in)
+}
+
+func (s *AccountService) Update(ctx context.Context, id int, in model.AccountInput) (*model.Account, error) {
+	if err := s.validate(in); err != nil {
+		return nil, err
+	}
+	return s.repo.Update(ctx, id, in)
+}
+
+func (s *AccountService) Delete(ctx context.Context, id int) error {
+	return s.repo.Delete(ctx, id)
+}
+
+func (s *AccountService) TotalPatrimony(ctx context.Context) (float64, error) {
+	return s.repo.TotalPatrimony(ctx)
+}