Guard auto-research public board claims

[huangruiteng]

Summary

• replace the stale auto-research public board fixture’s held-out/promotion-success wording with an explicit dev-only claim boundary
• keep held-out context and promotion/first-screen claims blocked unless separate authority exists
• update Frontstage types and smoke coverage so the board can render null holdout metrics and reject old 4.5x/promotion wording

Validation

• python3 -m json.tool docs/product/auto-research-frontstage-board.public.json >/dev/null
• npm run smoke:frontstage-route
• npm run build
• loopx check --scan-path docs/product/auto-research-frontstage-board.public.json --scan-path apps/dashboard/smoke/frontstage-route-smoke.ts --scan-path apps/dashboard/src/views/frontstage-auto-research-page.tsx --limit 200
• git diff --check

Preview

• Owner approved the local first-screen preview before commit/push per the repository gate.

[huangruiteng]

Self-review / maintainer note before self-merge:

Findings: none.

Product/architecture judgment:

• Motivation: the old auto-research board fixture could be read as a held-out improvement and promotion claim. This PR tightens that public surface into an explicit dev-only claim boundary.
• Solved or not: the JSON now carries auto_research_public_claim_boundary_v0, clears promotion candidates, nulls held-out metrics, and the smoke rejects the stale claim strings. That directly covers the risky public wording path.
• User/operator impact: the Frontstage board can still show useful dev-lane evidence while making held-out, promotion, and first-screen claims visibly gated.
• Main risk: presentation/public-claim semantics. I do not see runtime, permission, credential, raw-evidence, or private-state risk in this diff.
• Design judgment: this is a reusable boundary contract rather than a one-off text patch; the next cleaner step is to generate the fixture from live projection events, but this PR improves the current shipped surface safely.

Validation performed:

• git diff --check origin/main...HEAD
• python3 -m json.tool docs/product/auto-research-frontstage-board.public.json >/dev/null
• npm run smoke:frontstage-route
• npm run build
• loopx check --scan-path docs/product/auto-research-frontstage-board.public.json --scan-path apps/dashboard/smoke/frontstage-route-smoke.ts --scan-path apps/dashboard/src/views/frontstage-auto-research-page.tsx --limit 200

Merge decision: approved for authorized self-merge. Owner first-screen preview approval is recorded in the PR body / LoopX todo, and the focused validation is clean apart from the existing unrelated duplicate-index warning from loopx check.