feat: excluir transações de extrato + delete em lote por mês

Remove restrição que bloqueava delete de transações importadas.
Adiciona DELETE /transactions?month=YYYY-MM para exclusão em lote
e botão "EXCLUIR MÊS" na view de transações.

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

apps/api/internal/service/transaction.go

@@ -11,7 +11,6 @@ import (
 
 var (
 	ErrInvalidTransactionType   = errors.New("type must be 'income' or 'expense'")
-	ErrCannotEditImported       = errors.New("imported transactions cannot be edited or deleted")
 	ErrTransactionEmptyDesc     = errors.New("description is required")
 	ErrTransactionInvalidAmount = errors.New("amount must be greater than zero")
 )
@@ -55,11 +54,15 @@ func (s *TransactionService) Update(ctx context.Context, t model.Transaction) (*
 func (s *TransactionService) Delete(ctx context.Context, id int) error {
 	err := s.repo.Delete(ctx, id)
 	if errors.Is(err, repository.ErrNotFound) {
-		return ErrCannotEditImported
+		return errors.New("transaction not found")
 	}
 	return err
 }
 
+func (s *TransactionService) DeleteByMonth(ctx context.Context, month string) (int, error) {
+	return s.repo.DeleteByMonth(ctx, month)
+}
+
 func validateTransaction(t model.Transaction) error {
 	if strings.TrimSpace(t.Description) == "" {
 		return ErrTransactionEmptyDesc