simplify openenv.yaml: pure ASCII, remove all non-essential sections, copy yaml to WORKDIR in Docker

fix: use server.graders:... paths to match platform example format exactly

fix: align step_reward with grade_episode, pin deps, update docs, clean inference

feat: Iteration_3 — openenv validate PASS, wire compat, PayOpsReward, OPENAI_API_KEY- Fix completed, Docker verification alone pending- Padma