quiet-otters-dance.md

@primer/react-brand	minor

⚠️ Breaking change: Removed the imageBackgroundColor prop from River.Visual, RiverBreakout.Visual, and RiverBreakoutTabs.Visual.

The River gridline variant now applies the full-bleed visual background layout by default. Remove imageBackgroundColor="subtle" from River.Visual when using the gridline variant.

Remove imageBackgroundColor from RiverBreakout.Visual and RiverBreakoutTabs.Visual without replacement. Their default visual treatments are unchanged.

The background treatment is not applied to the default River variant or either RiverBreakout variant.

Updated the River gridline variant tablet layout with a 618px max-width and lateral gridlines.