handler: patch lerobot in-process (subprocess loses site-packages on HFIE)

add handler.py for stock-container HFIE deploy

v8: pin datasets==4.7.0 (4.8.x has broken hub.BucketNotFoundError import)

v7: phased install, force-reinstall hub==0.34.4, capture pip output

force-upgrade huggingface_hub during runtime install (datasets needs BucketNotFoundError)

runtime install of lerobot 0.5.1 via --ignore-requires-python

pin lerobot 0.4.4; strip 0.5.x-only config fields on load

handler.py + requirements.txt for folding_final on HFIE