feat(dialog-sdk): interactive zoom on ChartPreviewWidget with onChartViewChanged event

[pabloinigoblasco]

Motivation

In PJ 3.x, the FFT toolbox has a "Only data in zoomed area" mode where the user zooms in the embedded input chart and the FFT recalculates using only the visible range. The current Dialog SDK has ChartPreviewWidget for embedded charts, but it is static — no zoom, no pan, no events.

This PR adds interactive zoom to ChartPreviewWidget so plugins can replicate this behavior: the user zooms in the embedded chart, the plugin receives onChartViewChanged(), and reacts accordingly.

Summary

• WidgetData::setChartZoomEnabled(name) — plugin declares which charts should be interactive
• ChartPreviewWidget::setZoomEnabled() — enables rubber band zoom + mouse wheel zoom
• viewChanged() signal emitted on zoom/pan with the new axis range
• WidgetEventBuilder::chartViewChanged(x_min, x_max, y_min, y_max) — event JSON
• WidgetEvent::chartViewChanged() — parser with ChartViewState struct
• DialogPluginTyped::onChartViewChanged() — virtual for the plugin to override
• widget_binding wires viewChanged to the event callback in connectWidgetSignals()

Test plan

• Build pj_plugins — no compile errors
• Set setChartZoomEnabled("my_chart") — chart becomes zoomable (rubber band + wheel)
• Zoom the chart — onChartViewChanged fires with correct axis range
• Chart without setChartZoomEnabled — remains static (unchanged behavior)