France’s leftist New Popular Front, which won the most seats in high-stakes legislative elections earlier this month, said Tuesday it has selected Lucie Castets, a civil servant unknown to the public, as their candidate to be the new French prime minister. The announcement came shortly before President Emmanuel Macron is scheduled to appear in a nationally broadcast televised interview Tuesday evening, in hopes of ending weeks of political deadlock. Castets, a senior civil servant, graduated from Sciences Po, the London School of Economics, and the École Nationale d’ Administration. She…