feat(source-review): clarify Save→Confirm 2-step flow, remove Reviewer ID
- Relabel actions "Save review (step 1)" / "Confirm requirement (step 2)"
- Add step legend + "Step 2 · Create the requirement" panel and clearer outcome text so it is obvious Save is triage and Confirm creates the requirement
- Remove the Reviewer ID field (no auth/permissions yet); attribute reviews to a fixed studio_user actor in the audit trail
- styles: add .step-legend, drop now-unused .reviewer-field rules
Co-Authored-By: Claude Opus 4.8 noreply@anthropic.com