PARIS — The world’s most romantic river traces a long arc through Paris, a stunning backdrop to complement the magnificent City of Lights. For centuries, lovers have walked along the Seine River, crossed its bridges, stared into its eddies and ripples. They’ve hung locks on its bridges as a sign of their love, they’ve watched the reflections of golden streetlights waver in the Seine’s current. And while they do, they most definitely stay on shore.