kev-4b preview, decision-v7 recipe (transfer 0.790 dev / 0.806 locked; held-out pairs 0.73)

Research preview: Qwen3-4B-Base + LoRA r16, decision-v4, lr 5e-5 (trial lowdrift-4b-v4/01-trial-1); dev 0.843, transfer 0.759; locked test 0.852 / 0.794 (one ungated read)