- Add renderCollapsibleHeader() to renderer-registry
- Places chevron on right, spinner on left
- Toggles between ChevronRight (collapsed) and ChevronDown (expanded)
- Uses max-h-0/max-h-[2000px] with transition-all for smooth animation
- Dynamically adds/removes mt-3 to avoid margin when collapsed
- Update javascript-repl renderer to use collapsible sections
- Code and console output hidden by default
- Only file attachments remain visible
- 300ms smooth animation on expand/collapse
- Export renderCollapsibleHeader from web-ui index
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