Agent live card now uses the sentinel pattern to detect when it scrolls
out of view. When stuck, it collapses to a compact header bar with brand
styling and backdrop blur, with a ChevronUp button to scroll back.
When scrolled back into view, the card seamlessly expands to full view.
Also adds semantic colors to Sonner toast icons (success/info/warning/
error/loading) and fixes icon-to-text alignment in toasts globally.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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