The slab body covered the underlying zone fill almost completely —
`opacity: 0.85` (gray) and `opacity: 0.95` (white-on-select) drowned out
any zone color sitting beneath. Switched to independent `fillOpacity`
(0.6 unselected / 0.45 selected) and `strokeOpacity` (0.85 / 0.96) so
the outline stays crisp while the zone color reads through the fill.
On the selected state the hatch overlay carries the visual weight; no
need for an opaque white background underneath.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
