fix(grader): clamp scores to (0.01, 0.99) — platform requires strictly between 0 and 1

feat: multi-step env, pickle deserialization hard task, rebalanced difficulty

chore: production standardisation of the server codebase

Final submission readiness: cleanups, checklist, strict grader fix

chore: final calibration and validator fixes for OpenEnv submission

feat: finalize OpenEnv alignment and calibrate rewards for QA