fix(chunks): set position on remaining chunk insert paths

document_converters, the github size-fallback chunker, revert_service
restores, and the kb-persistence middleware now write explicit positions
(the middleware read path also orders by position).

surfsense_backend/app/tasks/connector_indexers/github_indexer.py

@@ -525,6 +525,7 @@ async def _simple_chunk_content(content: str, chunk_size: int = 4000) -> list:
                 Chunk(
                     content=chunk_text,
                     embedding=embed_text(chunk_text),
+                    position=len(chunks),
                 )
             )