DAMASCUS, Syria — Syrian government forces recaptured the ancient city of Palmyra on Sunday, scoring an important victory over Islamic State fighters who waged a 10-month reign of terror there and dealing the group its first major defeat since an international agreement to battle terrorism in the fractured nation took effect last year. The city known to Syrians as the “Bride of the Desert” is famous for its 2,000-year-old ruins that once drew tens of thousands of visitors each year before IS destroyed many of the monuments.