`fastvideo generate` takes a run config plus dotted overrides and never reads FastVideoArgs.add_cli_args, so the
documented `--h3-vae-nvfp4-decoder` flag failed before the model loaded. The flag is removed; the guide uses
`--generator.pipeline.experimental.h3_vae_nvfp4_decoder`, and a test drives that override through the generate parser
to FastVideoArgs. Also drops two narrating test docstrings.