Productize auto-research user gates

[huangruiteng]

Summary

• add explicit user-gate/takeover records to the auto-research experimental board projection
• render user gates on the experimental Frontstage auto-research route below the decision candidates
• update the showcase blueprint and route smoke so gates, metrics, promotion, and retirement remain visible

Boundary

• experimental auto-research route only
• does not change README, hosted Frontstage home, showcase index, hero, primary CTA, or other first-viewport entry points
• public fixture/projection text only; no raw logs, local paths, credentials, or private evidence

Validation

• python3 -m json.tool docs/product/auto-research-frontstage-board.public.json
• python3 examples/auto-research-artifact-contract-smoke.py
• npm run smoke:frontstage-route
• npm run build
• git diff --check