- Fix sync trigger: only fire on publish transition, not every PUT
- Add TestSyncOnPublish integration tests (2 tests, 16 total passing)
- Add group_label to frontend StepContent interface
- Guard Library Visibility select to procedure_step nodes only
- Block API edits to flow-synced steps (400 read-only guard)
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>