Get Layer Viz Stats

Whole-layer stats for one numeric column, for classed map styling.

breaks are the deduped ascending interior quintile boundaries (p20/p40/p60/p80); together with min/max they delimit up to five classes. Empty breaks with count 0 means the column has no non-null values. geometry_kind tells the client which classed styling applies (graduated circles for points, choropleth otherwise) — every layer carries both point and fill style layers, so the client cannot infer geometry from the style alone.