feat: announce closed public review via version banner

This PR replaces the open-public-review banners with a "public review has closed" banner on the UNTP specification pages, telling readers the review has finished, linking them to the public-review feedback issues, and stating the target 1.0 release.

The banner is driven entirely by the publicReview object in website/src/config/versions.ts. A new status: 'open' | 'closed' field selects between the existing open-review banners and the new closed-review banner, and issuesLabel and release supply the feedback-issues link and the announced release. When status is closed, both the reviewed version's pages (0.7.0) and the Work-in-Progress pages show the new info-style banner. The 0.6.0 pages are unaffected. A maintainer runbook for the config is added to .claude/CLAUDE.md, with a pointer to it from the config's JSDoc.

Test plan

• yarn build passes
• Closed banner renders on 0.7.0 pages and WIP pages
• 0.6.0 unmaintained banner unchanged
• "review comments" link resolves to the public-review-labelled issues