- MaterialPaintPanel owns its scroll: the eraser/reset row stays pinned and
the category tabs stick to the top, so only the material list scrolls.
- Selected catalog swatch + active scene-material card use the same
`ring-1 ring-primary ring-inset` outline as item/preset tiles.
- Choosing a material category auto-selects its first material.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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