A second-floor stair landing may seem like an odd spot to put a home office, but that’s where interior designer Ann Waldman likes to work. The trestle table she uses as a desk is pushed against the wooden balustrade, overlooking the stairs and a periwinkle-blue painting of two frolicking nudes by Portland artist Michele Russo. The light is lovely: a soft glow emanates from a skylight in the recessed ceiling and plays across sand-colored walls, imparting a sense of serenity. Lingering...