A new documentary by filmmaker Nathaniel Kahn is being called “a fierce yet tender reckoning with [architect] Louis Kahn’s complicated legacy. The film explores not just the gift and gravitas of the man’s global span of buildings, but also his mystery as a father.” The younger Kahn’s film is a direct and unapologetic effort to reconcile his father’s global reputation as a designer who gave his all to the world with the private scandal of a man who kept three different families in various corners of the world. It could have been a fruitless effort, but then, the younger Kahn met a Bangladesh architect who managed to put it all in perspective…