letsPlotJsVersion

Lets-Plot JS runtime version loaded by generated letsPlot{} iframes. Must match the lets-plot-common core version pulled in transitively by the lets-plot-kotlin-jvm artifact on the classpath (e.g. lets-plot-kotlin-jvm:4.14.0 → Lets-Plot core 4.10.1). Keep this in sync whenever the letsplot version in gradle/libs.versions.toml is bumped; the ConfigsTest "KSlidesConfig pins letsPlotJsVersion to the lets-plot core version" case pins the expected value. Overriding here avoids a library release when a compatible JS runtime is published upstream.