Fix Ralph acceptance snapshot drift

[codejeet]

Closes #379

Summary

• preserve the live pending Ralph completion override when plan-state is resnapshotted from SGT_PLAN.json
• keep declared terminal acceptance metadata only as forensics while Ralph remains unmet
• add a regression that exercises _plan_state_snapshot directly so stale verified acceptance cannot drift back in

Testing

• bash ./test_ralph_mode_config_and_state.sh
• bash ./test_plan_completion_acceptance_lifecycle.sh
• bash ./test_president_runtime_supervision.sh