fix: delete the DB row before the files in delete_document

File-first ordering meant a failed DB delete left a listed, 'completed'
document whose files were gone — and its surviving file_hash made
re-adding the same file dedup to the broken doc. DB-first (the order
delete_collection already uses) degrades the same failure to harmless
orphan files.

pageindex/backend/local.py

@@ -245,9 +245,6 @@ class LocalBackend:
 
     def delete_document(self, collection: str, doc_id: str) -> None:
         doc = self._require_document(collection, doc_id)
-        # DB row first, files after (same order as delete_collection): a failure
-        # mid-way then leaves harmless orphan files, not a listed document whose
-        # files are gone.
         self._storage.delete_document(collection, doc_id)
         if doc.get("file_path"):
             Path(doc["file_path"]).unlink(missing_ok=True)