feat(Accordion): add sticky flag to make headers sticky in ScrollArea

[syeo66]

Summary

Adds an opt-in sticky prop on Accordion.Root. When enabled, each Accordion.Header pins to the top of the nearest scrolling ancestor (e.g. a ScrollArea) while its item is in view, then is pushed out by the next item's header — the classic sticky-section-header pattern.

<ScrollArea maxHeight={300}>
    <Accordion.Root sticky>
        <Accordion.Item value="…">
            <Accordion.Header>…</Accordion.Header>
            <Accordion.Content>…</Accordion.Content>
        </Accordion.Item>
        {/* … */}
    </Accordion.Root>
</ScrollArea>

Default is false, so existing usages are unchanged.

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🦋 Changeset detected

Latest commit: 5e73c9b

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This PR includes changesets to release 3 packages

Name	Type
@frontify/fondue-components	Minor
@frontify/fondue	Patch
@frontify/fondue-rte	Patch

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[noahwaldner]

We should probably add some functionality for scroll restoration. Because of the changing vertical size of each item, the active item vanishes when collapsing. In long sections (like theme settings) this would seem confusing to the user.

Measuring if the current scroll position is bigger than the Accordion.Headers distance from the top of the accordion would tell us if the item is in "sticky state". We could then manually set the scroll position so it's still top aligned after closing.

The difficulty with this would be to get the current scroll position if the scrollarea is added by the consumer

Video to demonstrate the issue.
https://github.com/user-attachments/assets/a8df4a49-b82a-4c33-bb31-f9c1aefe9546

[syeo66]

We should probably add some functionality for scroll restoration. Because of the changing vertical size of each item, the active item vanishes when collapsing. In long sections (like theme settings) this would seem confusing to the user.

@noahwaldner I think I got a reasonable solution now

[github-actions]

Lead time: 22 hours, 38 minutes, 22 seconds (22.64 total hours) from first commit to close.
Review time: 22 hours, 36 minutes, 48 seconds (22.61 total hours) from ready for review to close.

• First commit: 11.5.2026, 14:19:59.
• Ready for review: 11.5.2026, 14:21:33.
• Closed: 12.5.2026, 12:58:21.