Android login hangs on "generating sign in code..." when browser is Firefox

### Describe the Bug

After completing OIDC authorization in the browser, the app stays on "generating sign in code..." indefinitely. The success page fires an Android deep link via window.location.href = "intent://auth-success#Intent;scheme=pangolin;package=net.pangolin.Pangolin;end" — but Firefox on Android silently ignores intent:// URIs (this scheme is Chrome-only). The app never receives the callback and never polls for the session token.
Server side completes correctly: deviceWebAuthCodes shows verified=1 with the correct userId populated. Zero network traffic from the device after the OIDC redirect — the app is simply never signaled.

### Environment

- Pangolin: 1.17.1
- Android app: latest (Play Store)
- Browser: Firefox for Android (reproduced); Chrome for Android (works)

### To Reproduce

1. Open the Pangolin Android app → tap Sign In
2. When the browser opens, complete OIDC authorization (Authentik)
3. Browser reaches the success page
4. App remains on "generating sign in code..." spinner indefinitely

### Expected Behavior

App receives the deep link callback, polls /api/v1/auth/device-web-auth/poll/, and completes login.