chore: upgrade Changesets CLI to v3 with changesets/action v2

[willeastcott]

Summary

The Changesets CLI and changesets/action majors have to move together:

• Action v2 refuses CLI v2. That broke the release workflow in chore(deps): update changesets/action action to v2 #340, which fix: revert changesets/action to v1 #342 reverted.
• Action v1 can't handle CLI v3. v1 finds what was published by matching New tag: lines in the publish output, and v3 no longer prints them (it prints Created git tags:). Packages would still reach npm, but no git tags would be pushed and no GitHub releases created, with no error.

This PR does both at once. It's also the last reason #348 isn't safe to merge: #348 bumps the CLI to v3 on its own.

Changes

• @changesets/cli 2.31.1 → 3.0.3, and changesets/action v1 → v2.
• Renamed action inputs for v2: commit-message, pr-title, publish-script and create-github-releases. v2.1.2 fails outright on the old names.
• Dropped the GITHUB_TOKEN env var from the release step. v2 takes its token from the github-token input (the default GitHub token) and passes it to the publish script itself. It also fails if the env var ever differs from that input.
• Removed the Renovate hold on changesets/action.
• .changeset/config.json: $schema now points at @changesets/config 4.0.1, the version CLI v3 uses. The config validates against it unchanged.

Verification (local)

• Tags and GitHub releases: action v2 reads the published packages from an NDJSON file named by CHANGESETS_OUTPUT. That variable reaches the CLI through pnpm -w changeset on pnpm 12, and the CLI wrote the file. If it didn't, v2 would only log a warning and skip tags and releases.
• Publishing: CLI v3 publishes with pnpm publish --json --access … --tag … --no-git-checks, the same command already dry-run on pnpm 12 in chore: upgrade pnpm to v12 #349. changeset publish-plan, which uses pnpm 12's pnpm info, correctly reports nothing new to publish.
• Version PR: changeset version produces the same bumps (@playcanvas/react 0.11.6, @playcanvas/blocks 0.3.10), changelog entries and formatting under CLI v2 and v3 for the pending changeset.
• Other checks: build, lint, test and the Prettier check pass. The lockfile only swaps CLI v2's dependency tree for v3's, all from the npm registry with integrity hashes.

After merging

The next push to main runs action v2 for real. Because a changeset is pending, it will update the open version PR #339, which uses the same changeset-release/main branch. Merging #339 is then the first publish on the new setup. Check that npm shows provenance for both packages, and that the git tags and GitHub releases were created.

Merge this before #348. Renovate will then drop @changesets/cli from #348.

No changeset: release tooling only.

🤖 Generated with Claude Code

[changeset-bot]

⚠️ No Changeset found

Latest commit: 7ea35ea

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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commit: 7ea35ea