Add kind/breaking label for breaking changes in release notes

[Mark90]

Summary

Breaking changes are currently invisible in the generated release notes — they land in 🚀 Features or ♻️ Refactors like any other PR. This adds a dedicated kind/breaking label and a ⚠️ Breaking Changes section.

• .github/release.yml — the section is listed first. Since a PR lands in only the first matching category, a PR that is both a feature and a breaking change is listed as breaking rather than under Features. That is intentional: it is the section people read when upgrading.
• .github/labels.sh — kind/breaking in red (b60205) instead of the kind/* blue, so it stands out on the PR list.
• .github/pull_request_template.md — a checklist item noting that a breaking change belongs in a major release and that the PR summary should describe the upgrade path, since it ends up in the release notes.

Notes

GitHub's release-notes config is static and cannot key off the version being cut, so "only for major releases" is not directly expressible. The section is self-gating instead: it only renders when a PR in the release range actually carries the label.

.github/labeler.yml is deliberately untouched — breaking-ness cannot be derived from file paths, so it stays a human call like kind/feature vs kind/bug. The require-release-label check already accepts any kind/* prefix, so no workflow change was needed.

The label has already been created in this repo via .github/labels.sh. The same change is going out to orchestrator-core, nwa-stdlib, oauth2-lib and pydantic-forms so the four repos stay consistent.

Type of change

• I have set a kind/* label describing the change — kind/ci, applied automatically from the changed paths.
• If this is a breaking change, I have set kind/breaking. — n/a

Checklist

• I have updated relevant documentation. — the PR template and inline config comments.
• My code follows the style guidelines of this project.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.52%. Comparing base (1215f71) to head (faaf061).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #79   +/-   ##
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  Coverage   94.52%   94.52%           
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  Files          33       33           
  Lines         731      731           
  Branches       71       71           
=======================================
  Hits          691      691           
  Misses         31       31           
  Partials        9        9           

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