Rename `total` → `totalElements` for Spring-Page parity and add three new required paging fields: pageNumber, pageSize, totalPages. Adds a `paged( slice, pageable, totalElements)` factory alongside the existing single-page `of(list)` shortcut. Enables offset pagination of /documents search (#315). Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>