Update README.md

Add dataset card

Prune internal/dead fields from route4.json (domain labels, construction-pipeline leftovers)

Prune internal/dead fields from route3.json (domain labels, construction-pipeline leftovers)

Prune internal/dead fields from route2.json (domain labels, construction-pipeline leftovers)

Prune internal/dead fields from route1.json (domain labels, construction-pipeline leftovers)

Remove fs_bundle: shipped via GitHub repo instead

Add fs_bundle sandbox assets for route1

Add route4.json (challenging 644-task subset)

Add route3.json (challenging 644-task subset)

Add route2.json (challenging 644-task subset)

Add route1.json (challenging 644-task subset)

initial commit