Support controlled state in the carousel component

[oscarcarlstrom]

Introduce controlled selection for the <Carousel> component, allowing external management of the selected index.

This way it is possible to use for example query params to decide where the Carousel should start. Or auto-scroll with setTimeout:

Screen.Recording.2025-11-13.at.12.08.09.mov

My initial thought was to consolidate the onSelectedIndexChange and the onChange callbacks. The onChange callback was initially added to support tracking, and this is used by some consumers already. I haven't found any easy way to make the onSelectedIndexChange callback flexible enough to support both CarouselItem | number (for tracking you probably want CarouselItem, but for regular controlled state management the index (number) is much easier. The callback also needs to be of type SetStateAction, since the next/prev "buttons" bases the new state set on the current state. A simple approach would be to just scrap onChange altogether, but then that would require the consumer to put the component in a controlled state just to be able to track changes. Which also feels a bit much to ask. So I suggest we initially just keep the onChange prop for tracking purposes, and separate that from controlled state management.

[changeset-bot]

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Latest commit: 4b048bd

The changes in this PR will be included in the next version bump.

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Name	Type
@obosbbl/grunnmuren-react	Patch

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