fix: treat sticky elements as scrollable ancestors, not fixed

[clauderic]

Fixes #1756

Summary

The isFixed utility was returning true for both position: fixed and position: sticky elements. In getScrollableAncestors, when an isFixed element was encountered, traversal would stop immediately and fall back to document.scrollingElement — bypassing any actual scrollable containers in between.

This is correct for position: fixed (which is positioned relative to the viewport and has no scrollable DOM ancestors), but incorrect for position: sticky. Sticky elements remain part of the normal document flow and still scroll with their nearest scroll container. Treating them as fixed caused autoscroll to skip the actual scrollable ancestor (e.g. a scrollable table container) and use the document scroll element instead, breaking horizontal autoscroll in sticky table headers.

The fix removes position: sticky from the isFixed check so sticky elements are treated normally during scroll ancestor traversal.

Test plan

• Set up a sortable list inside a position: sticky table header with a horizontally scrollable container
• Drag a column header toward the edge of the visible area
• Verify that the container scrolls horizontally as expected

---

Automated fix by Claude Code

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🦋 Changeset detected

Latest commit: 5f34fed

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

This PR includes changesets to release 10 packages

Name	Type
@dnd-kit/dom	Patch
@dnd-kit/abstract	Patch
@dnd-kit/collision	Patch
@dnd-kit/geometry	Patch
@dnd-kit/helpers	Patch
@dnd-kit/react	Patch
@dnd-kit/state	Patch
@dnd-kit/vue	Patch
@dnd-kit/solid	Patch
@dnd-kit/svelte	Patch

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commit: 5f34fed