Add metadata about items in queue

For debugging it would be good to add some metadata about who queued an item and when it was queued.

## Acceptance Criteria
- I can interrogate the queue and see who queued items and when

Start by locating the queue implementation and its existing item representation, then inspect how items are queued, stored, and exposed for interrogation. Trace the relevant tests or entry points before deciding where the queuing identity and timestamp belong. Done means queued items expose who queued them and when, as described by the acceptance criterion.

Written by the indexing model from the issue text.