feat(files): dedupe by stem|ext + oo projects files dedupe

- FileDedupKey groups true duplicates (same name+extension)
- put-md --replace deletes matching stem|ext only (not other formats)
- oo projects files dedupe PROJECT_ID [--apply] [--cross]
- Cross-folder mode prefers non-_trash folders, keeps newest file

Co-authored-by: Cursor <cursoragent@cursor.com>

README.md

@@ -611,6 +611,9 @@ oo projects files upload 33 ./notes.docx
 oo projects files download 12345 --to ./copy.docx
 oo projects files rename 12345 notes-v2.docx
 oo projects files delete 12345
+oo projects files dedupe 7              # dry-run duplicate report
+oo projects files dedupe 7 --apply      # remove older stem|ext copies per folder
+oo projects files dedupe 7 --cross --apply  # cross-folder; keep non-_trash
 
 # Agent document pipeline (md in git ↔ docx in OO; OCR scans)
 oo docs tools