After more than 20 years at Vidal Sassoon, styling hair and managing operations in London and North America, Peter Bradley teamed with Sassoon colleague Dirk Diegel to launch an upscale establishment in Boston, where the German-born Diegel had been based for 14 years. Dubbed “a salon that transcends trends and celebrates individual beauty,” the pair’s two-year-old eponymous business makes its home on the second floor of a typical row house in the city’s tony Back Bay neighborhood. The spare yet comfortable space, designed by Studio Luz Architects, not only communicates the owners’ mission; it provides a well-lighted, functional arena for