fix: address review feedback on batch-size default, requirements-local, docstring

- NOTIFICATION_QUEUE_BATCH_SIZE default reverted to 0 (unlimited) -- the
  existing behavior before this ticket, so deployments must opt in to the
  cap rather than having it silently applied at 5000
- requirements-local.txt: bump sientia_do pin to 1.12.3 to match requirements.txt
- Trim the load_latest_data docstring addition so it reads as documentation,
  not a changelog entry

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/orchestrator/utils/test_connectors_config.py

@@ -84,7 +84,7 @@ def test_build_mongo_db_config_with_defaults():
         'connection_string': 'mongodb://root:wKZDbMNU1c@localhost:27018',
         'database_name': 'sientia',
         'ttl_index_seconds': 3600,
-        'notification_queue_batch_size': 5000,
+        'notification_queue_batch_size': 0,
     }