Chinese carmakers are already beating their Western rivals when it comes to winning over the country’s middle-class drivers. Now they are coming for rich customers looking to add a little extra to their cars.Xiaomi last month started a service that will allow buyers to customise their 529,900 yuan (US$74,000) SU7 Ultra racer electric sedans with select trim and paint jobs – adding at least 100,000 yuan to the sticker price.A major smartphone designer that is making quick inroads with its...