Add fallback to parent_entity_id for backward-compatible deletes

[felixschmetz]

Summary by cubic

Make Qdrant bulk deletes backward-compatible by matching parent IDs on both original_entity_id (new) and parent_entity_id (old). Uses a should filter so either field triggers deletion, preventing missed records during sync.

^{Written for commit 38582d3. Summary will update automatically on new commits.}