feat: scene ghosting, as the client streams a zone's scenes

The client keeps the scene under the player loaded, the scenes the zone
file's transitions connect to it, and the global scene
(Zone::StreamScenesAroundPosition 0x0108a3f0, TerrainManager::GetSceneAtPos
0x01069010, the connected scenes at 0x01066500; transitions naming a
missing scene dropped as Zone::FixupInvalidTransitions 0x010842e0 does).

- ZoneScenes (dCommon): the terrain's scene map lookup and the scene graph,
  shared by the world server and the dashboard.
- Objects remember the scene they were placed in (spawners pass theirs on).
- ghosting_scenes=1 (world config, off by default): players get the objects
  of their loaded scenes instead of the ones within the ghosting distances;
  objects from no scene go by the scene under them. Zones without a scene
  map keep distance ghosting.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

dZoneManager/Level.h

@@ -15,13 +15,15 @@ public:
 	};
 
 public:
-	Level(Zone* parentZone, const std::string& filepath);
-	
-	static void MakeSpawner(const SceneObject& obj);
+	// sceneID: the scene id of the zone scene the file is (EntityInfo::scene of its objects)
+	Level(Zone* parentZone, const std::string& filepath, int32_t sceneID = -1);
+
+	static void MakeSpawner(const SceneObject& obj, int32_t sceneID = -1);
 
 	std::map<uint32_t, Header> m_ChunkHeaders;
 private:
 	Zone* m_ParentZone;
+	int32_t m_SceneID = -1;
 
 	//private functions:
 	void LoadSceneObjects(const std::vector<SceneObject>& objects);