bmild/nerf ? reverse-engineered prompt

Build me a working NeRF demo from this repo that I can run locally without having to figure out the details myself. I want to be able to download the example data, train on the Fern or Lego scene, watch training in TensorBoard, and then render new views from the trained model. Please make the setup as smooth as possible, with clear instructions that actually work from a fresh machine, and fix anything that would stop the notebooks or scripts from running end to end.

If there are any missing steps for the example data, weights, or environment setup, please handle those too. I’d also like the mesh extraction notebook to work on a trained model, so include anything needed for that flow. Keep the result faithful to the original project, but make it easier to run and try out. If you need to check current docs or dependencies online, go ahead and do that.