uSync.Umbraco.Commerce — Umbraco 18 upgrade and repo standards

Repo: Jumoo/uSync.Umbraco.Commerce

Upgraded to Umbraco 18 / Umbraco Commerce 18.1.0 on v18/main — pure package-version bump, no code changes needed
Added repository standards (CODE_OF_CONDUCT, SECURITY, CHANGELOG, CLAUDE.md, editorconfig, Directory.Build.props, GitVersion, locked packages.lock.json) and GitHub Actions CI/CD (PR build, package build, NuGet trusted-publishing release, CodeQL) via PR #11, merged
Ported the same repo standards to the v17/main line via PR #12, merged — 17.x-specific version numbers and lock file, code unchanged
Verified both PRs' dotnet-build.yml checks actually ran and passed in CI, not just locally