torch is only needed for the PyTorch training utilities (GlitchDataset,
train_gan, save/load_checkpoint). Import it inside a try/except so that
inference and plotting utilities (plot_q_transform, whitened_snr_scaling)
work without torch installed. Guards added to each torch-dependent function.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>