VPN disconnects over time

### Describe the Bug

I just set up a new Pangolin setup and are mostly happy, a few important features are already posted as feature requests.
But the Android App doesn't really work for me. I need the VPN to be always connected, regardless of where I am. So when the network changes from wifi to mobile eg.
But just at home I experienced, that the VPN was disconnected after some time. I even tried pinning the app which didn't seem to help much.
One important point is, that I cannot enable "Always-on VPN" for Pangolin in the Android setting. Always used that for Tailscale and Netbird and it worked flawlessly. Maybe this is a first point to try if this fixes it.

### Environment

- OS Type & Version: Debian 13 VPS
- Pangolin Version: 1.15.4
- Gerbil Version: latest (at the time of this issue)
- Traefik Version: latest (at the time of this issue)
- Newt Version: latest (at the time of this issue)
- Client Version: 0.1.6

### To Reproduce

Connect the Android VPN and leave it a few hours, maybe even change the network.

### Expected Behavior

It should stay connected + I should be able to force it stay connected using the Android settings.