Walmart Inc. is offering annual stock grants as a new incentive for store managers, bringing potential pay for the most successful ones to more than $400,000. Starting in April, all US store managers will receive as much as $20,000 in Walmart stock every year, as the world’s largest retailer seeks to attract and retain staff. The amount of stock grants will vary by store format, with those overseeing smaller outlets eligible for less, the company said Monday....