Sitting on a jerry-rigged table made from a crude slab of Douglas fir positioned atop two stumps, Ken Otter explains how his mobile milling business helps West Marin residents give their fallen or dying wood a second life. He holds up his hands, which lack the calluses and folds that most carpenters have—“computer hands,” as he calls them. He’s had many careers, and woodworking is the newest. He says it’s a meditative practice, but one…