Fix torchaudio CUDA mismatch: install via PyTorch cu121 index in pre-install.sh

torchaudio from plain pip installs CPU/wrong-CUDA build causing
libcudart.so.13 error on ZeroGPU. Install via the PyTorch CUDA 12.1
wheel index to match the pre-installed torch on the worker.

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

pre-install.sh

@@ -1,2 +1,4 @@
 pip install -U setuptools
 mim install mmcv>=2.0.0
+# Install torchaudio matching the pre-installed PyTorch/CUDA build on ZeroGPU
+pip install torchaudio --index-url https://download.pytorch.org/whl/cu121

requirements.txt

@@ -16,4 +16,3 @@ spaces==0.48.1
 gradio==5.25.0
 pydantic==2.8.2
 av
-torchaudio