SPRINGFIELD — The state’s top court has ruled wrongful-death claims can be added to a malpractice suit even after the statute of repose has expired.Illinois’ Supreme Court unanimously held Thursday that the plaintiffs in the case could use the legal rule that softens time limits for amended pleadings if they stem from the same course of conduct that was originally alleged.Justice Charles E. Freeman authored the unanimous decision, finding that the relation-back doctrine — which allows new claims to …