cuFFT does not support bfloat16. mel_converter was being moved to device
without an explicit dtype, inheriting bfloat16 from the model context.
Force float32 for both mel_converter.to() and wav.to() so the STFT
inside the mel converter runs in a supported dtype.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>