Add LeRobot v3.1 language annotations (task aug, plan, timestamped subtasks) and handle details

Document per-episode annotations in dataset card

Add success and annotation_notes columns to episode metadata

Add per-episode task descriptions, success labels, and tracking-quality notes

Cleaned copy of willlyb/snack_transfer@3e0388ba4c6efe7731731bf9b9184d34f19afb79

initial commit