Add piper pi05 checkpoint

Add piper pi0 checkpoint

Add piper single-arm LeRobot dataset (4 tasks, 125 episodes, 71,702 frames)

Restructure: g2/{model,dataset} to make room for piper

Add pi0 G2 dual-arm checkpoint (30k steps) + model card

Add G2 dual-arm LeRobot v2.1 dataset (58 episodes, 48,332 frames, 10 Hz)

initial commit