New Delhi: Sara Ali Khan’s appointment as Kalyan Jewellers’ brand ambassador is the latest addition to a celebrity strategy that has evolved over more than a decade from one national face into a network of Hindi and regional film stars. Khan joins Amitabh Bachchan and Katrina Kaif in the company’s nationally visible ambassador line-up. She will appear in campaigns across television, digital, print, outdoor and Kalyan Jewellers’ stores. However, …