Yamandú Orsi, a telegenic left-leaning former mayor and history teacher, has taken office as Uruguay’s new president. On Saturday in a swearing-in ceremony, he took the helm of a government that has pledged to strengthen the social safety net while reversing years of economic stagnation. The inauguration of Orsi, 57, marks the return of Uruguay’s Broad Front — a center-left mix of moderates, communists and hardline trade unionists — after a five-year interruption by the country’s outgoing conservative president, Luis Lacalle Pou. The ceremony came three months after Orsi’s presidential victory in a remarkably civilized election race between two moderates, praised as an antidote to the polarization gripping the region.