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/Packages/packages-lock.json

@@ -147,6 +147,15 @@
       },
       "url": "https://packages.unity.com"
     },
+    "com.unity.ai.navigation": {
+      "version": "2.0.9",
+      "depth": 0,
+      "source": "registry",
+      "dependencies": {
+        "com.unity.modules.ai": "1.0.0"
+      },
+      "url": "https://packages.unity.com"
+    },
     "com.unity.ai.toolkit": {
       "version": "1.0.0-pre.12",
       "depth": 2,