- File mode: Search API KQL pagination matching SearchService pattern
- Folder mode: CAML FSObjType=1 via SharePointPaginationHelper.GetAllItemsAsync
- MakeKey composite key (name+size+dates+counts) matches DuplicatesServiceTests scaffold
- Groups only items with count >= 2, ordered by group size then name
- ExtractLibraryFromPath derives library name from path relative to site URL
- SelectProperties added per-item (StringCollection has no AddRange)
