- Add 'section_header' to VALID_STEP_TYPES in backend validation so
procedural flows with section headers can be published
- Replace procedural editor's inline tag input with TagInput component
(supports autocomplete, Tab, comma, semicolon, and paste splitting)
- Add semicolon delimiter support to TagInput component
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>