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/bridge/mod.rs

@@ -102,7 +102,8 @@ pub fn generate_snapshot(
         day: time.day(),
         time_of_day: time.time_of_day_minutes(),
         day_phase: time.day_phase(),
-        paused: time.paused,
+        paused: time.paused(),
+        tick_rate: time.tick_rate,
     };
 
     tracing::trace!(
@@ -111,12 +112,13 @@ pub fn generate_snapshot(
         visible.len()
     );
     buffer.snapshot = Some(ObserverSnapshot {
-        version: 3,
+        version: 4,
         tick: time.tick,
         game_time,
         player_facing: FacingDirection::default(),
         entities: visible,
         visible_tiles: Vec::new(), // Empty until #112 adds LOS filtering
+        nearby_interactions: Vec::new(),
     });
 }