Despite fall’s chill blanketing Manhattan, opera-goers are delighting in the light-hearted comedy in Juilliard’s production of Mozart’s “La Finta Giardiniera.” Composed when he was just shy of turning 19, Mozart indulges in the fiery emotions that stir a garden party, gathered at the house of a small-town mayor. The opening scene reels in the listener while two maids whisper about {…}