Volcano Plot: optional significance / effect-size thresholds with cut-off lines and up / down / not-significant coloring #9039

Feature Summary

The Volcano Plot operator (common/workflow-operator/src/main/scala/org/apache/texera/amber/operator/visualization/volcanoPlot/VolcanoPlotOpDesc.scala) renders a plain px.scatter of effect vs -log10(p) with color=$effectColumn, color_continuous_scale="RdBu" (:113-121). Two things are missing that make it a volcano plot rather than a scatter plot:

1. No threshold lines. Readers expect a horizontal line at the significance cut-off (e.g. padj = 0.05 → y = 1.30) and vertical lines at ±effect cut-off (e.g. |log2FC| = 1). Without them you cannot read from the figure whether anything is significant. In our DE run every padj was ≈ 0.999, so the whole plot sat between y = 0.00007 and y = 0.00028, and nothing on the figure showed that y = 1.3 was the bar to clear.
2. Color carries no information. The point color is the effect-size value, which is already the x coordinate. The usual convention in volcano-plot tooling (EnhancedVolcano, ggvolc, bullkpy) is categorical: points that pass both cut-offs are colored by direction (up / down) and everything else is muted.

Proposed Solution or Design

Three optional properties, all off by default so saved workflows render as today: a significance threshold (dashed horizontal line at -log10 of it), an effect-size threshold (dashed vertical lines at ± it), and a "Color by significance" toggle that, when both thresholds are set, colors points Up (p below the cut-off and effect above +threshold), Down (p below the cut-off and effect below −threshold) or Not significant, with a legend, instead of the continuous scale. Both thresholds apply to whichever p-value column the user selected.

Affected Area

No response