ci: migrate release workflow to changesets/action v2

[Bccorb]

Problem

@seamless-auth/types@0.20.0 published to npm on a green Release run, but no v0.20.0 git tag and no GitHub Release were created.

Dependabot bumped @changesets/cli from 2.31.1 to 3.0.2 in #57, while release.yml still pinned changesets/action@v1.

The v1 action detects what got published by scraping changeset publish stdout for New tag: lines:

let newTagRegex = /New tag:/;
for (let line of changesetPublishOutput.stdout.split("\n")) {
  if (line.match(newTagRegex)) {
    await git.pushTag(`v${pkg.packageJson.version}`);
    await createRelease(octokit, { pkg, tagName });

The v3 CLI replaced that output format. The publish log for the failing run shows:

🦋 changeset v3.0.2
◇  Successfully published:
@seamless-auth/types@0.20.0
◇  Created git tags.

No New tag: line, so the regex matched nothing, releasedPackages stayed empty, and neither pushTag nor createRelease ran. The step still exited 0, so the workflow stayed green.

This mismatch is called out in the action's own v2.0.0 notes: "Validate that projects use Changesets CLI v3 and direct Changesets CLI v2 users to changesets/action@v1."

Fix

Move to changesets/action@v2, which reads published packages from the CHANGESETS_OUTPUT file rather than stdout, and is the version built against the v3 CLI.

Input renames required by v2:

v1	v2
version	version-script
publish	publish-script
createGithubReleases	create-github-releases

Two env entries are dropped:

• GITHUB_TOKEN: v2 no longer reads it, and the github-token input already defaults to the workflow token.
• NPM_TOKEN: v2 removed its own .npmrc handling, so npm auth relies solely on the .npmrc that actions/setup-node writes from NODE_AUTH_TOKEN (already configured via registry-url).

Notes

• No changeset: this touches only .github/, not src/, so there is nothing to publish.
• v0.20.0 is already on npm. Its tag and GitHub Release are being backfilled by hand, since this fix only repairs future releases.

Checks

npm run typecheck, npm run lint, npm run format:check, and npm test (233 tests, 17 files) all pass locally on Node 24.