Render the function-tree category roots as a Build-style square-tile grid
(icon when available, otherwise a two-letter abbreviation) with a hover
tooltip for the full name, so the Items and Build panels read the same.
Share one TooltipProvider with disableHoverableContent + the icon-grid
tooltip class to avoid the flicker when moving between adjacent tiles.
Legacy fallback panel category bar wraps instead of scrolling horizontally.
Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>
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