Add soundfile as explicit dependency

soundfile was only a transitive dep of torchaudio but collect_all()
in PyInstaller can't bundle it if it's not installed. Adding it as
an explicit dependency ensures it's in the venv and bundled correctly.

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

python/pyproject.toml

@@ -15,6 +15,7 @@ dependencies = [
     "pysubs2>=1.7.0",
     "openai>=1.0.0",
     "anthropic>=0.20.0",
+    "soundfile>=0.12.0",
 ]
 
 [project.optional-dependencies]