Mirrors _sync_attachments. Idempotent dedup keyed on
(parentItemID, title) so re-syncing is a no-op. Wired into both
the create-item and update-existing-item branches of push_to_zotero.
Adds 'notes' counter to the stats dict.
Fixes test_sync_deeper mocks: both _sync_attachments and _sync_notes
call store._con().execute(); updated the MagicMock side_effect to
route by SQL fragment so the notes query returns [] while attachment
queries return the fixture rows.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
e204ea0e4c