One of Turkey’s most famous prisoners made his final appeal for freedom on Friday, at the culmination of a years-long trial that has come to define Ankara’s tense ties with Western allies in the wake of a failed 2016 coup. Paris-born activist and philanthropist Osman Kavala was a relative unknown when he was detained on his arrival at Istanbul’s airport from a trip to a cultural centre in the Turkish city of Gaziantep in October 2017. But his continued imprisonment without a conviction has turned the 64-year-old into a hero for President Recep Tayyip Erdogan’s opponents- and a focus of Western…