Field: per-cell DOMINANT family colour (was a mean of all overlapping hues →
brown mud); mixed/overlap zones now fade by 'purity' instead of muddying.
Tuned colourful-but-subtle behind the dots (desaturate 0.40 + slight lift to
white, maxα 0.44) — dots stay the stars.
Zoom/pan: wheel to zoom at cursor, drag to pan when zoomed, +/−/reset controls
(top-left) + double-click reset; dots grow with zoom; field & hit-testing follow
the view transform, clipped to the plot rect.
