Apple Inc. will get an observer role on OpenAI’s board as part of a landmark agreement announced last month, further tightening ties between the once-unlikely partners.Phil Schiller, the head of Apple’s App Store and its former marketing chief, was chosen for the position, according to people familiar with the situation. As a board observer, he won’t be serving as a full-fledged director, said the people, who asked not to be identified because the matter isn’t public....