reward_ckpts layout

Each reward model keeps its own directory:

hpsv2/
- open_clip_pytorch_model.bin
- HPS_v2.1_compressed.pt
pickscore/clip_processor/
- CLIP tokenizer/processor files for laion/CLIP-ViT-H-14-laion2B-s32B-b79K
pickscore/model/
- PickScore v1 model weights (pytorch_model.bin or model.safetensors)
open_clip/
- optional extra OpenCLIP weights downloaded to the old flat root
aesthetic/
- sac+logos+ava1-l14-linearMSE.pth
geneval/
- mask2former_swin-s-p4-w7-224_lsj_8x2_50e_coco_20220504_001756-743b7d99.pth
ocr/
- reserved for OCR reward assets if needed

Run bash download_reward_ckpts.sh to download the PickScore and HPSv2.1 assets used by L2P_NFT.