In winter, Heidelberg Opera decamps a few miles to the old court theatre of Schwetzingen Palace, a cool and lovely eighteenth-century confection of gilt and swirly blue marble, for some baroque indulgence. This year’s show was a Neapolitan version by composer Leonardo Vinci (no relation) of the Dido story, brought to London by Handel as impresario in 1737, tricked out with arias by other composers and staged as a showcase for his new superstar Italian castratos at Covent Garden. Conductor Wolfgang Katschner, who made this new edition with director Yona Kim, is touring it round Germany and it will play at the Halle Festival there in May.It has a complicated genesis, but the script was written by Pietro Metastasio, an amazing craftsman, expert at putting a few characters into an airle