[6.x] Fix card designer preview element type

[riasvdv]

Description

Card designer preview requests omitted the element type because it is stored in designer settings rather than the serialized layout config. Include it in the preview request so the backend can render the sample element, while preserving generated fields and the saved layout value.

Extracts only the card preview request fix from #19665.

[github-actions]

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[github-actions]

This PR had conflicts with 6.x. Claude attempted an automatic resolution and pushed a merge commit. Please review the merge commit carefully before approving/merging.

Claude's response

The merge is done and committed as c6b15f2. It hasn't been pushed.

CHANGELOG.md was the only file with a conflict, and it wasn't ambiguous. Both sides had added a different bug-fix line at the same spot in the list:

• This branch added the card designer preview fix ([6.x] Fix card designer preview element type #19776).
• 6.x added the reactive element-editor controls fix ([6.x] Connect element editor reactive layout refreshes #19769).

I kept both lines, this branch's first, so no CONFLICT-REVIEW comment was needed. The other changed files came in from 6.x without conflicts, and I didn't edit them.

Changed

• Combined the two changelog entries in CHANGELOG.md, staged it, and ran git commit --no-edit to finish the merge.

Found

• Nothing.