feat: Implement NavMesh pathfinding and Deep Social visuals

- Phase 20-F: NavMesh Integration
  - Added 'com.unity.ai.navigation' package
  - Implemented Runtime NavMesh Baking in EnvironmentManager
  - Added NavMeshObstacle to environmental assets
  - Updated AgentVisual to use NavMeshAgent for movement
  - Implemented 'Instinctive Avoidance' via target offsetting

- Phase 21: Social Interaction & Expressions
  - Added procedural Dance and Wave animations in AgentAnimator
  - Implemented 'Dance Party' triggering logic in engine.py and AgentVisual
  - Added social relationship syncing (Backend -> Frontend)
  - Implemented proximity-based social greetings (Heart emote + Wave)
  - Updated Models.cs to support relationship data parsing

unity-client/Assets/Scripts/GameManager.cs

@@ -90,8 +90,11 @@ namespace TheIsland.Core
                     if (agent.IsAlive) count++;
                 }
                 return count;
+                return count;
             }
         }
+        
+        public Dictionary<int, AgentVisual> AllAgentVisuals => _agentVisuals;
         #endregion
 
         #region Unity Lifecycle