In mobile browser, EC won't use headset audio

### Steps to reproduce

0. Connect bluetooth headset to phone. Test that it works for media playback from other apps.
1. Join a call, in a browser.
2. Get a brief burst of call audio from headset, then audio output switches to the phone.
3. In audio settings, attempt to switch "Speaker". Only option is "Default".

### Outcome

#### What did you expect?

Audio comes out of headset - or that it is at least an option.

#### What happened instead?

Audio from phone

### Operating system

Android 13

### Browser information

Chrome 118.0.5993.81

### URL for webapp

call.element.io

### Will you send logs?

No

Start by reproducing issue #1830 on Android 13 with Chrome 118, using call.element.io and a Bluetooth headset. Inspect the mobile call audio-routing and settings behavior described in the report; done means headset audio remains available during the call and is offered as an output option.

Written by the indexing model from the issue text.