Enable third-person camera collision against BlockCam layer only

- Main: Deoccluder CollideAgainst = BlockCam (256), CameraRadius 0.01,
  HeroCutout.replaceDeoccluderPullIn off (re-enables AvoidObstacles at runtime)
- Lobby: Floor moved to BlockCam layer

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Assets/Scenes/Lobby.unity

@@ -744,7 +744,7 @@ GameObject:
   - component: {fileID: 968374000}
   - component: {fileID: 968373999}
   - component: {fileID: 968373998}
-  m_Layer: 0
+  m_Layer: 8
   m_Name: Floor
   m_TagString: Untagged
   m_Icon: {fileID: 0}