fix(doc): update caption references when copying node items

[qianchongyang]

When add_node_items or insert_node_items copies items from one document to another, the caption, reference, and footnote references were not being updated to point to the new document's items. This caused captions to reference stale indices from the source document.

This fix tracks the old->new index mapping as items are copied and uses the existing _update_refitems_with_lookup method to update all references after copying.

Fixes: #2298

[github-actions]

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