feat(simulation): add proximity detection and interaction verbs

Implement compute_nearby_interactions system that detects entities
within close (≤2) and mid (≤5) Manhattan distance, computes
available verbs per D-060 spec. NPCs get Talk+Observe at close
range, Observe-only at mid range; PersonOfInterest flips priority.
Objects get Examine. Results populate nearby_interactions[] on
ObserverSnapshot v4. Bump protocol version 3→4. Implements #404.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/perception/interpretation.rs

@@ -199,6 +199,7 @@ mod tests {
         world.init_resource::<crate::knowledge::KnowledgeEventQueue>();
         world.init_resource::<EntityRegistry>();
         world.init_resource::<ObservationEventQueue>();
+        world.init_resource::<crate::simulation::interaction::NearbyInteractionBuffer>();
         world
     }