chai1: add chai-lab's structure token-pair weights (diffuser/chai1_structure_token_pair/{weights,bias}, diffuser/chai1_structure_bond/weights) - the second halves of input_projs.TOKEN_PAIR and bond_loss_input_proj, which chai-lab's diffusion module reads as its pair input. Every existing parameter byte-identical; JAX loads them unused. Needed by LocalFold's native CUDA port, which reads these blobs.