model card: shorter, author name

model card: simplify, single author

model card: describe v4 only, drop the v1/v2 comparison

v4: add README.md

v2 at root, v1 in v1/; simplify the model and performance sections

Drop hand-crafted from the feature description

Document v1 and v2; replace the pre-leak-fix accuracy table with verified v2 numbers

Upload README.md with huggingface_hub

initial commit