Add an option to disable audio ducking when notifications arrive

### Checklist

- [x] I have used the search function for [**OPEN**](https://github.com/AntennaPod/AntennaPod/issues) issues to see if someone else has already submitted the same feature request.
- [x] I have **also** used the search function for [**CLOSED**](https://github.com/AntennaPod/AntennaPod/issues?q=is%3Aissue+is%3Aclosed) issues to see if the feature was already implemented and is just waiting to be released, or if the feature was rejected.
- [x] I will describe the problem with as much detail as possible.
- [x] This request contains only one single feature, **not** a list of multiple (related) features.

### App version

3.11.0f

### Feature or improvement you want

When using AntennaPod on Android 16, incoming system notifications cause the app to duck (lower) the currently playing media volume. This behavior is quite disruptive, especially when listening to podcasts at lower volumes or in noisy environments.

Other media apps on Android allow users to disable audio ducking entirely, keeping playback volume unchanged when notifications appear. It would be very helpful if AntennaPod could provide a similar option.

### Why should this be added?

An optional setting that allows users to disable audio ducking so that playback volume remains constant when notifications arrive.

### Screenshots / Drawings / Technical details

_No response_