OnlyOffice converts legacy binary Office uploads (.xls/.doc/.ppt) into
OOXML (.xlsx/.docx/.pptx) on the server. UploadToFolderReplacing matched
by the exact stem|ext via FindFilesByDedupKey, so a repeated
`oo dav upload FOLDER f.xls --replace` never found the stored f.xlsx and
appended a second file (live: ids 3799+3887, 3800+3888).
- EquivalentUploadExt / FindFilesByStemExt: match by stem with a
legacy↔OOXML extension equivalence, so .xls finds the saved .xlsx.
- planUploadReplacement: pick the surviving file and the redundant
duplicate ids for a replacing upload.
- UploadToFolderReplacing updates the existing file in place (UpdateFile,
stable id, no delete window), removes extra duplicates, and falls back
to conversion-aware delete + upload when the portal rejects the update.
- AssertNoFileConflict (--no-replace) uses the same conversion-aware
matching so a .xls upload conflicts with an existing .xlsx.
- Offline tests cover the matcher, the plan and the repeated-.xls
regression; pdf/xlsx behaviour unchanged.
