Reorganize project folders and clean up editor tooling

Move editor scripts to Assets/Scripts/Editor (PlaySceneWindow, SceneCollection),
move DefaultNetworkPrefabs and the Main Camera custom blends asset into
Assets/Settings, and shelve the unused HeroCutout shader/include under
Assets/Unused. Rename the Chameleon background texture, delete the obsolete
DefaultParentForEditor script and New Lighting Settings asset, add a The Room
SceneCollection asset, and drop the redundant Assets menu entry from the
StraightenKnees tool.

Assets/Scripts/Editor/SceneCollection.cs

@@ -0,0 +1,42 @@
+using System.Collections.Generic;
+using System.Linq;
+
+using UnityEditor;
+using UnityEditor.SceneManagement;
+
+using UnityEngine;
+
+namespace Chameleon.Editor
+{
+    [CreateAssetMenu(menuName = "Chameleon/Scene Collection (Editor)")]
+    public class SceneCollection : UnityEngine.ScriptableObject
+    {
+        public List<SceneAsset> sceneAssets = new();
+
+        [UnityEditor.Callbacks.OnOpenAsset]
+        public static bool OnOpenAsset(int instanceID, int _)
+        {
+            var @object = EditorUtility.EntityIdToObject(instanceID);
+            if (@object is SceneCollection sceneCollection)
+                sceneCollection.Open();
+            return false;
+        }
+
+        public void Open()
+        {
+            if (sceneAssets.Count == 0)
+                return;
+
+            OpenScene(sceneAssets.First(), OpenSceneMode.Single);
+
+            foreach (var sceneAsset in sceneAssets.Skip(1))
+                OpenScene(sceneAsset, OpenSceneMode.Additive);
+        }
+
+        static void OpenScene(SceneAsset sceneAsset, OpenSceneMode mode)
+        {
+            var scenePath = AssetDatabase.GetAssetPath(sceneAsset);
+            EditorSceneManager.OpenScene(scenePath, mode);
+        }
+    }
+}