feat(website): add localized release notes

[Natsummerance]

Summary

• Add localized /release-notes/ pages for ReadMD v2.3.7-beta.4 in English, Simplified Chinese, Traditional Chinese, and Japanese.
• Cover presentation isolation, update integrity, startup loading, tab state, touch targets, beta boundaries, platform assets, and checksum guidance.
• Expand root/localized AI corpora and sitemap from 40 to 44 canonical URLs.
• Extend browser smoke and clean-network production checks to all 44 routes.

Approvals

SEO intent / release accuracy / release engineering: 9.89 / 9.86 / 9.81; final decision meeting 9.87 (release_notes_approval.json).

Validation

• npm run verify:release: green across 44 canonical URLs.
• Browser smoke: 44/44 routes passed, including four new localized release-notes pages.
• Release API: v2.3.7-beta.4 is published with 11 assets; SHA256SUMS.txt returns HTTP 200.