ci(release): release next from a dedicated branch and restore requireCommits

[Upd4ting]

Summary

Adopt the branch-bound npm release channels introduced in the org reusable workflow (AntelopeJS/.github#10, merge commit f4ce81591d09d271a480fd796e12a725cc973e0f): latest is released only from the default branch and next only from a branch named next. The workflow now passes --git.requireBranch=<branch> to release-it and, on latest, ignores prerelease tags when computing the changelog and version.

• .github/workflows/release.yml: bump the pinned reusable workflow from e541e89 to f4ce815. Inputs, secrets and permissions are unchanged (channel choice latest/next).
• .release-it.json: remove git.requireBranch (the workflow is now the single source of truth for the release branch). git.requireCommits was already true and stays so.
• CONTRIBUTING.md: add a short "Releases" section pointing to the org-wide Release channels guide.

Same change as AntelopeJS/antelopejs#155 and AntelopeJS/api#52.

Related issue

Follow-up to AntelopeJS/.github#10.

Verification

• pnpm lint, pnpm format:check, pnpm knip, pnpm prepack (build): pass.
• pnpm test: pass (184 passing).
• actionlint .github/workflows/release.yml (rhysd/actionlint Docker image): no findings.
• CI=true pnpm exec release-it --ci --dry-run --no-npm.publish --no-github.release --no-git.requireUpstream --git.requireBranch=ci/next-branch-releases: exits 0. The config parses, requireCommits passes (commits exist since v0.1.7), and release-it proposes 0.1.7...0.1.8 with the expected changelog. The local package.json version bump from the dry run was reverted; no release was triggered.

Checklist

• The pull request title follows Conventional Commits.
• I added or updated tests when behavior changed. N/A: CI configuration only.
• I updated documentation when users or contributors are affected.
• I documented breaking changes and migration steps. N/A: no breaking change.
• I did not include credentials or unrelated changes.