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/DefaultNetworkPrefabs.asset

@@ -1,36 +0,0 @@
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---- !u!114 &11400000
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-  m_Name: DefaultNetworkPrefabs
-  m_EditorClassIdentifier: Unity.Netcode.Runtime::Unity.Netcode.NetworkPrefabsList
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