A battle of billionaires is brewing on the Las Vegas Strip, with casino mogul Steve Wynn’s ex-wife alleging boardroom recklessness as she asks a court to give her control of company stock that she left in his hands five years ago. Elaine Wynn filed court documents Monday seeking access to more than $900 million worth of stock and providing an inside glimpse at her ex-husband’s dealings with Kazuo Okada, a former business partner with whom Wynn Resorts Ltd. has waged a legal battle since 2012.