The Huntington Theatre Company had an opening-night after-party on Wednesday for its Southie-set production “Good People,” written by South Boston native David Lindsay-Abaire. The night doubled as a celebration of the Huntington’s 30th birthday, so there was plenty of cake and champagne to go around. The guest list for the festivities included Boston Foundation president Paul Grogan, Boston University College of Fine Arts dean Benjamin Juarez, chef Barbara Lynch, “Good People” director and Acton native Kate Whoriskey, Representative Gloria Fox. The party went on until midnight and included a performance by Hayley Jane and the Primates. “Good People” runs through Oct. 14.