fix: pin gradio==5.49.1 + huggingface_hub<1.0 (Jinja2 bug in Gradio 4)

fix: pin huggingface_hub<1.0 (HfFolder removed in 1.0)

fix: drop audioop-lts, pin gradio<5

fix: pin gradio>=5 + audioop-lts shim for py3.13

Initial commit: agent-stack live demo