Classic miniKanren Peano arithmetic on (:z / (:s n)) naturals. pluso runs
relationally in all directions: 2+3=5 forward, x+2=5 → 3 backward,
enumerates the four pairs summing to 3. *o is iterated pluso. lteo/lto
via existential successor decomposition.
19 new tests, 188/188 cumulative. Phase-tagged in the plan separately
from Phase 6 CLP(FD), which will eventually replace this with native
integers + arc-consistency propagation.