fix: gate autonomous queue on eval score

[fazxes]

Summary

• add an eval-score gate to the autonomous builder prompt so sub-80 real-repo evals force eval-related normal-priority work
• mirror the new scheduling rule in daemon/operations docs and record fresh Phractal evaluation Harden Nightshift from live validation runs #13
• add prompt-contract regression coverage for the new gate

Test plan

• make check
• bash scripts/validate-docs.sh
• python3 -m pytest tests/test_nightshift.py -k 'evolve_prompt_step_zero_targets_the_cloned_repo or evolve_auto_prompt_has_eval_score_gate' -v