ST. PETERSBURG — A pair of tall drag queens is performing on a stage, cracking jokes and interacting with the only three guests who have come to this gay bar on a Thursday night. The entrance to this renowned venue is marked only by a nondescript metal door in a dimly lit courtyard. “We could hardly find it,” complains one of the guests, a woman with a short-cropped haircut who was visiting from the Moscow region. Since the Russian Supreme Court banned the “international LGBT movement” in late November, an atmosphere of unease has settled over St. Petersburg’s gay nightlife scene and pushed it…