test(research-radar): require bench handoff fields

[t3chn]

Summary

• Expand the Research Radar experiment proposal template with explicit Agent Bench Lab handoff fields.
• Add a unittest that keeps the template and Codex prompt aligned with required proposal and handoff fields.
• Include the new contract test in the deterministic test script.

Issue

• N/A

Test plan

• python3 -m unittest tests.test_research_radar_experiment_proposal_contract
• scripts/run-deterministic-tests.sh