MOSCOW — Russian President Vladimir Putin on Wednesday declared his intention to seek re-election next March, a vote he appears certain to win. If Putin serves another six-year term that would run through 2024, it would make him the nation’s longest serving ruler since Soviet dictator Josef Stalin. The president chose to make the long-expected announcement at the GAZ automobile factory in Nizhny Novgorod, where he found an enthusiastic audience in the workers. “I couldn’t find a better place and moment for that,” he said, to massive applause.