docs: add violin plot thumbnail and CHANGELOG PR ref

Replace the placeholder box_plot.png thumbnail for the Violin Plots recipe
with a generated 1024x680 violin image, and add the #412 reference to the
CHANGELOG entry.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: jqnatividad

CHANGELOG.md

@@ -7,7 +7,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/) a
 
 ### Added
 
-- Add `Violin` trace type with box, mean line, KDE span, and split/grouped support
+- [[#412](https://github.com/plotly/plotly.rs/pull/412)] Add `Violin` trace type with box, mean line, KDE span, and split/grouped support
 - [[#406](https://github.com/plotly/plotly.rs/issues/406)] Expose `plotly.js` 3.1–3.6 attributes
 
 ### Changed

docs/book/src/recipes/img/violin_plot.png

@@ -6,5 +6,5 @@ Kind | Link
 :---|:----:
 Error Bars |[![Scatter Plots](./img/error_bars.png)](./statistical_charts/error_bars.md)
 Box Plots | [![Line Charts](./img/box_plot.png)](./statistical_charts/box_plots.md)
-Violin Plots | [![Violin Plots](./img/box_plot.png)](./statistical_charts/violin_plots.md)
+Violin Plots | [![Violin Plots](./img/violin_plot.png)](./statistical_charts/violin_plots.md)
 Histograms | [![Scatter Plots](./img/overlaid_histogram.png)](./statistical_charts/histograms.md)