zones_set / zones_clear / zones_merge, zones_contains / zones_nearest and the clusters' bounding circles,
over fixed arrays of ZONES_MAX (16). WildlifeWorld.active freezes an animal outside (no state change, no
dice), NpcWorld.active a walker (and no birth outside), VehicleWorld.active a moored boat, and
ThingsWorld.restocks keeps a morning's restock inside; every default is "everywhere", so an unbound game
is unchanged. Tests: the merge (near players one cluster, far two, a player leaving splits a chain),
contains, nearest, the radius; wildlife, npc, vehicles and things pass as before.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
