40e962db89
First half of the #281 clock-enable set: Sign promotes the private sign0() semantics to vocabulary (strict comparisons; NaN and -0.0 fall to 0.0), Select is the stateless 2:1 mux that consumes Bool back into the F64 plane. Both zero-arg, Firing::Any, rostered (count pins 29→31); an engine E2E drives both through the real GraphBuilder→compile→run seam. refs #281