In the children’s section of Albertine, copies of “Le Petit Prince,” stories of Tintin and Babar and other much-loved French classics are for sale beneath a sapphire-colored ceiling gilded with hand-painted constellations. What’s arguably New York’s most enchanting bookstore opened a decade ago inside the palatial Payne Whitney House, an early 1900s landmark built by the architect Stanford White on the southeast corner of East 79th Street and Fifth Avenue that’s served as the headquarters of the French Embassy’s cultural and educational activities in the United States for the past 72 years.