Nominated for five Oscars, including best picture, “Lady Bird” (⋆⋆⋆⋆; rated R) is a dazzling collaboration between two of the most impressive art-house actresses of the past decade. Saoirse Ronan plays the awkward but brilliant title character, an artistically inclined high school girl aiming for something better, while Greta Gerwig makes her debut as solo writer/director. Like “Rushmore” and “Juno,” this is a rare delight of honesty and humor that covers the highs and lows and magic of teenage life.