It is a bittersweet rite of passage in Hollywood: once-popular actors, waking up to fine lines and fewer good roles on offer, start making the rounds of charity events, with the possibility of scooping up a product endorsement along the way. So unforgiving is an industry known to treat even Oscar winners like yesterday’s muffin that the swift rise and steady decline of former actress Meghan Markle’s foray into multimedia stardom was sadly predictable.