feat: add support for lowercase Hugging Face Space secrets

feat(kaggle): add clean_launch.py + shrink budget to 20/25/30 = 75 eps

feat(kaggle): default to fixed-budget curriculum 20/30/50 episodes

fix(grpo): skip reference model when kl_beta=0 to save 5GB VRAM on T4

fix(kaggle): align pip-managed numpy with kernel's loaded numpy

fix(kaggle): pin torch via constraints file in REPAIR cell

fix(kaggle): escape backslash-n in REPAIR cell separator print

chore(kaggle): rebuild notebook v3 + clean dev-scratch files