If you thought the Middle East was stagnant, think again. The Gulf economies are among the richest and most vibrant on the planet, helped by a Brent crude oil price that rose back to over $90 per barrel this week. A $3.5trn fossil-fuel bonanza is being spent on everything from home-grown artificial intelligence models and shiny new cities in the desert, to filling the coffers of giant sovereign-wealth funds that roam the world’s …