Sleep timer required for audio playback

When reading in an audio book, one feature that has been requestid is to have a sleep timer.

The need for this is when a user is listening and they fall asleep. The reading system when left untouched for a user designated amout of time would turn off. This makes it easy for the user to go back in time to where they fell asleep. This has been a feature in DAISY reading system for decades!

The user would turn on or off the sleep timer. It can be set for 15 minutes, 30 minutes etc.

The user can then go back by that amount of time to get approximately where they fell asleep. In practice, this works by the user going back by the amount they set for the sleep timer and then moving forward until they can tell where they left off.

If this is implemented with read aloud, I think it would be on the reading system to know where they started reading and giving the ability to go back to that location.

No files, tests, or entry points are identified. First locate the existing audio and read-aloud playback controls, then clarify timer choices, stopping behavior, and how returning to the starting location should work. Done requires an agreed implementation scope and acceptance criteria.

Written by the indexing model from the issue text.