- Error(w, err) now extracts PlatformCode() from *xerrors.Err and
includes "platformCode" in the JSON body when set; omitted otherwise
- errorBody updated to accept platformCode as an explicit parameter
- Upgraded code.nochebuena.dev/go/xerrors dependency to v0.10.0
- Added two new tests: platformCode included when set, omitted when absent
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>