Android client stuck on "Waiting for browser" after successful Login Flow v2 approval (Android 16)

### Steps to reproduce

1. Install the latest stable Nextcloud Android app from Google Play.
2. Launch the app and log in successfully to one Nextcloud account.
3. In the app, choose "Add account" to add a second account.
4. Enter the Nextcloud server URL.
5. Continue with the browser-based login (Login Flow v2).
6. Approve the login in the browser (on-device or on a PC browser).
7. Browser displays "Account connected".
8. Switch back to the Android Nextcloud app.

The app remains indefinitely on "Waiting for browser".

### Expected behaviour

After approving Login Flow v2 in the browser, the Android app should:
- Poll the `/login/v2/poll` endpoint
- Retrieve the generated credentials (app password)
- Complete account setup automatically

### Actual behaviour

The browser login completes successfully and displays "Account connected".
However, the Android app remains indefinitely on "Waiting for browser" and never completes login.

This occurs for:
- Normal browser login
- Login approval performed on a PC browser
- Login attempted using a device/app password

The app appears to wait for a browser callback that never occurs, and does not proceed after successful server-side flow completion.

### Android version

Android 16 (SDK 36)

### Device brand and model

Google Pixel 7 Pro

### Stock or custom OS?

Stock

### Nextcloud android app version

versionCode: 30350090 / 3.35.0

### Nextcloud server version

30.0.17

### Using a reverse proxy?

Yes

### Android logs

Relevant logcat excerpts:

The app launches Login Flow v2:

START u0 {act=android.intent.action.VIEW dat=https:///login/v2/flow/ ...}

Browser completes login and shows "Account connected".

Android app returns to foreground:

D/AuthenticatorActivity: onStart()
D/AuthenticatorActivity: onResume()

However, no completion occurs and the app remains on "Waiting for browser".
No nc:// deep link callback is received or processed.

### Server error logs

```bash
No server-side errors observed.
The server correctly completes Login Flow v2 and confirms "Account connected".
```

### Additional information

- The issue occurs when adding an additional account to the app.
- At least one existing account is already logged in and functioning normally.
- The problem reproduces consistently when attempting to add another account.
- EDIT: Seems login with QR code works