Retrieve the full metadata record for a specific LOC digital item. Returns contributors, subjects, summary, languages, locations, rights information, physical description, call number, original and online formats, access restrictions, former catalog IDs, notes, related items, and links to digital resources (TIFF, JPEG, PDF) for items with digital surrogates. Use after libofcongress_search on a result whose is_item is true. Pass the result id verbatim — it may be a simple ID or a slash-separated newspaper path; do not prepend the loc.gov URL. Non-item results (is_item: false) — collections, exhibits, guides, newspaper pages — have no item record and cannot be retrieved here.