[codex] docs: promote README version cleanup to main

[jeremymcs]

Summary

Closes #542

• Promote the README version-source cleanup from merged PR [codex] docs: align README version source of truth #543 onto main.
• Cherry-picks the exact docs changes so main gets the npm/package metadata source-of-truth wording without pulling unrelated next changes.
• Uses the allowed chore/backmerge-* branch pattern for a main-targeted promotion PR.

Root Cause

PR #543 landed on next, but the same README version-conflict cleanup is needed on main so public stable documentation does not continue showing stale legacy release/current-stream signals.

Validation

• git diff --check HEAD~1..HEAD
• GITHUB_BASE_REF=main npm run lint:docs -- --json
• Stale README/current-stream grep returned no matches for old release/canary claims.

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Note

Low Risk
Markdown-only wording and link/index updates; no runtime, install, or auth behavior changes.

Overview
Documentation-only promotion that stops advertising specific repo release numbers (e.g. v1.39.0 / v1.42.x) as the current product version across README (EN + JA/KO/PT/ZH) and docs/README.md.

Localized READMEs rename versioned “highlights” sections to feature highlights, drop links to old GitHub release tags, and add a shared note that @opengsd/gsd-core on npm / package.json is canonical while docs/ release files are legacy continuity only. Several locale lists also remove the manual canary workflow bullet so stable docs don’t imply an active canary install path.

The English README reframes the “returning user” callout toward @opengsd/gsd-core@latest (instead of “see CHANGELOG for what’s new”) and replaces the v1.42.1 release-notes pointer in Getting Started with the same canonical-version guidance. The docs index drops pinned RELEASE-v1.42.x entries, retargets What’s new / preview quick links to latest / next npm tags, and labels CANARY docs as archived maintainer notes.

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