Returns a single reconciliation record by id, including its matches (matches_as_a,
matches_as_b), the records it is matched against (matched_records), the remaining
amount_to_be_reconciled, and whether it is exhausted. The embedding vector is omitted.
Non-admin callers only see records of their companies.

Note: the record is looked up with find_by (not find_by!), so an unknown record_id
does not return a 404 — the endpoint responds 200 with a null body.