ci: pin the shared workflows to @v2, and finish the changesets v3 move

[unional]

Fixes the red release job on main.

What broke

changesets/action v2 renamed its inputs and refuses to run against @changesets/cli v2. The shared release workflow was pinned at @main in repobuddy/.github — which is that repo's v1 line — where Renovate had already auto-merged the action to v2.1.1, so the mismatch arrived here uninvited:

Error: The following inputs have been renamed:
- "publish" -> "publish-script"
- "version" -> "version-script"
- "commit" -> "commit-mesage"

What this does

Renovate has since landed @changesets/cli v3 (5467b92) and @changesets/changelog-github v1 (23a5ad0) on main. This PR is what those bumps left undone:

• All repobuddy/.github refs @main → @v2. That repo keeps parallel v1/v2 lines; v2 is the one pairing changesets/action@v2 with CLI v3. pnpm-docs.yml and setup-playwright are byte-identical between the two, so only the release path changes behavior.
• .changeset/config.json schema → @changesets/config@4.0.0. Every key in use survives into v4 unchanged, including both ___experimentalUnsafeOptions_* keys.
• root engines.node >=22.6.0 → ^22.11 || ^24 || >=26, the v3 floor. The root package is private, so nothing published changes.

Going forward rather than pinning the action back to @v1: CLI v2 also hits the npm 12 npm info --json change, where .versions reads undefined, every version looks unpublished, and the release republishes into an E403.

Supersedes #842, which pinned to @v1 — the hold rather than the upgrade.

Verified

• pnpm exec changeset status runs clean on cli 3.0.1
• no changeset tag or --sinceMaster callers; nothing else wraps changeset version
• lockfile unchanged against main

No changeset file — CI and devDependency metadata only.

Paired with repobuddy/.github#50, which puts that repo's main back on changesets/action@v1 for the consumers still on CLI v2.

🤖 Generated with Claude Code

[changeset-bot]

⚠️ No Changeset found

Latest commit: 24f4871

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.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR