Add smplfitter and chumpy wheels

Remove gradio_rangeslider (requires gradio<6, conflicts)

All deps in requirements.txt; remove all runtime pip install and patch logic

Add all Wan2GP core deps to requirements.txt at once

Add diffusers to requirements

Fix Gradio launch: remove module-level chdir, skip Wan2GP pip install

Initial Sulphur-2 image-to-video Gradio Space