i15-1: Setup & Queue interaction improvements

A number of improvements can be made between the `Setup` and `Queue` pages.

- [x] Currently queue tasks are added to the beginning of the queue, they should be added to the end by default
- [ ] "Playlist" item order from the setup page is not always preserved when added to the queue. Ordering commonly observed to shift when there is a task in progress in the queue, but seems stable if the queue is empty

Start by examining the Setup and Queue pages and reproduce adding a Playlist while a queue task is in progress. Compare the Playlist order from Setup with the resulting queue order; done means the items retain their Setup order in both an empty queue and a queue with an active task.

Written by the indexing model from the issue text.