iOS: enhancement: more convenient way to change input gain?

**Describe the bug**

iOS's automatic scaling of input volume doesn't always work as well as one might expect. If you're using an input device that runs quiet--e.g. an external Bluetooth headset or wired USBC ADC (and doesn't present its input level in the iOS Control Centre > Jamulus Settings), at present your best way to turn the default gain up is to open up GarageBand, set your mic gain, close GarageBand, and reopen Jamulus. This is a pain.

Would it be possible to have access to whatever setting GarageBand is making right inside Jamulus as part of the usual Settings sheet?

**Operating system**

iOS 26.4.2

**Version of Jamulus**

3.12

No file, test, or entry point is identified in the issue. Begin by tracing Jamulus's iOS Settings sheet and its input-gain handling, then determine whether the GarageBand-controlled setting is exposed to Jamulus. Done means providing a documented in-app way to adjust quiet input devices, with coverage for the reported iOS cases.

Written by the indexing model from the issue text.