The rail was a fixed Row(center, max) — one button per tab — so adding
the Search tab pushed it 54px past its width and threw a RenderFlex
overflow. Center the icons when they fit and scroll horizontally when
they don't (LayoutBuilder + SingleChildScrollView + a minWidth floor),
so the rail stays correct at any tab count. (T-200)
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
jpmschweitzerandClaude Opus 4.8
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