[WC-3594]: Chart previews no longer overlap other widgets in design mode

[samuelreichert]

Pull request type

Bug fix (non-breaking change which fixes an issue)

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Description

In Studio Pro design mode, the preview of the Area, Bar, Bubble, Column, Heat map, Line, Pie/Doughnut and Time series charts overflowed narrow containers (e.g. a col-4 layout grid column) and overlapped the neighbouring widgets.

Cause: the shared ChartPreview rendered the chart with fixed widths (385px with legend, 300px without) and the plot image with a fixed 300px width, inside an inline-flex wrapper. When the container was narrower than that, the content overflowed visibly on top of the next column.

Fix (minimal, preview only):

• Root wrapper is now display: flex with max-width set to the previous size (385px / 300px).
• The chart area uses width: 100%, so it fills the available width up to that cap.
• The plot image can shrink (flex: 1 1 0; min-width: 0) and the legend keeps its 85px width (flex: none).

When there is enough room, the preview keeps its current size (385×232 / 300×232). It only shrinks when the container is narrower. The runtime chart is not affected. Custom chart uses its own preview and is not affected either.

Also added a unit test for ChartPreview and an Unreleased → Fixed changelog entry to each affected chart package.

What should be covered while testing?

1. In Studio Pro design mode, add a layout grid with three col-4 columns. Put a Line chart in the first column and a Text widget in the second.
   • Before: the chart overlaps the Text widget.
   • After: the chart stays inside its column.
2. Add the chart using both the "+" icon and drag and drop.
3. Toggle "Show legend" (and "Show scale" for the Heat map). The legend should stay fully visible and the plot should shrink.
4. In a full-width column, the preview should look the same as before.
5. Quick check of the other affected charts: Area, Bar, Bubble, Column, Heat map, Pie/Doughnut and Time series (including the range slider image).

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