If it weren’t for Keegan Swenson, John Gaston would be a Leadville legend. Heading into the 2026 Leadville Trail 100 MTB, the Aspen athlete — known mostly for his ski mountaineering exploits — held three second-place finishes over the past four years, picking up bronze in his only other appearance. In Saturday’s swan song, the 39-year-old did what he’s always done: ignore the pre-race narrative, quietly hammer out a new script and — eventually —…