Marine Le Pen, the French far-right leader, in Paris on July 7, 2024. Le Pen, whose far-right party leads polls in France, was convicted in 2025 of embezzlement. The outcome of her appeal will determine if she can run for president. (Mauricio Lima/The New York Times) By MARK LANDLER and SÉGOLÉNE LE STRADIC Marine Le Pen, the French far-right leader and a front-runner to win next year’s presidential election, on Tuesday lost her appeal of an embezzlement conviction, prolonging more than a year…