Add v1 reviewer readiness gate

[stacknil]

Summary

• Adds a v1 readiness gate to the top-level reviewer pack
• Links the gate from README and roadmap so consolidation criteria are easy to find
• Extends reviewer-doc tests to protect the gate, artifact contract, and no-platform boundary

Validation

• pytest tests/test_reviewer_docs.py --basetemp .pytest-artifacts-readiness-gate
• pytest --basetemp .pytest-artifacts-full-20260528-1
• git diff --cached --check

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 533ca30b23

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

Allow documented final-demo additions in the gate

When maintainers follow the still-present optional final demo path in docs/roadmap.md and README, this new gate says v1 consolidation requires the four-demo matrix to stay stable and only allows documented retirements. That makes the linked checklist contradict the roadmap/README guidance that one more demo may be added before v1, leaving no valid documented path for an allowed fifth demo even if its docs, tests, and artifacts are updated.

Useful? React with 👍 / 👎.