docs: update README counts to reflect 217 task release

data: drop login_required tasks (220 -> 217)

docs: clean README — drop references to non-public mirror

docs: refresh README for v3.0 (single task.jsonl, 220 tasks, no scenario_tier)

v3.0: consolidate to task.jsonl (L1+L3, 220 tasks); drop scenario_tier field

Restore L1 dataset robustness tags.

Upload l1.jsonl

Upload folder using huggingface_hub

initial commit