RS-Claw: Progressive Active Tool Exploration via Hierarchical Skill Trees for Remote Sensing Agents. - Liangtian Liu; Zeyuan Wang; Ziyu Li; Kai Ouyang; Zichao Tang; Chengfu Liu; Haifeng Li; Hanwen Yu; Wentao Yang; Cheng Yang; Dongyang Hou (CoRR, 2026)