Chart.js 4: make legends static by default but keep click-to-toggle on one chart

Chart.js legends toggle datasets on click by default. That is wrong for paired charts (dumbbell, grouped bars), where hiding one series breaks the comparison.

To disable it globally while letting one chart opt back in, save the built-in handler before overriding it:

let toggleLegend: any;
const legend = Chart.defaults.plugins.legend;
toggleLegend = legend.onClick;   // built-in show/hide handler
legend.onClick = () => {};

Then in the one chart that should toggle:

plugins: { legend: {
  onClick: toggleLegend,
  onHover: (e) => (e.native.target.style.cursor = "pointer"),
  onLeave: (e) => (e.native.target.style.cursor = "default"),
} }

The saved default handler works per chart because it uses this.chart. To verify in Playwright without access to chart instances, sweep clicks down the canvas top-left and compare canvas screenshots before and after: only the toggling chart changes.