feat(rag): wire retrieval-augmented chat into chat_fn

feat(chat): stream tokens as they're generated

fix(space): cast model weights to fp16 to keep cpu-basic worker alive

fix(model): sync ghostlm package to v0.9 (SwiGLU + RMSNorm + RoPE)

feat: ship v0.9 chat (81M, CTIBench 28.9% / CTF 59.2% / SecQA 39.3%)

chore: squash history to reclaim LFS storage from removed checkpoint