[PM-38801] `Congstar`: passkey does not work

### Origin

Native Application (non-browser app)

### Web URL or App name

sso.congstar.de

### Passkey Action

- [x] Creating new passkey (Registration)
- [ ] Signing in (Authentication)

### Build Information

© Bitwarden Inc. 2015-2026

Version: 2026.4.2 (21562)
📱 samsung SM-A176B 🤖 16@36 📦 prod
🧱 commit: https://github.com/bitwarden/android/commit/2e88a418a11a042fed230a0871cdcaa9bbff0c04
💻 build source: bitwarden/android/actions/runs/25866701011/attempts/1
🦀 SDK: 2.0.0-6825-release-hotfix-v2026.4.1-bwpm
🌩 Server: 2026.5.0 @ EU

### Additional Information

Passkey: `Congstar` presumably does not support third-party providers (like Bitwarden) and only allows a single key to be stored.

In the past, however, creating and logging in using Google's passkey worked without any problems.

### Issue Tracking Info

- [x] I understand that work is tracked outside of Github. A PR will be linked to this issue should one be opened to address it, but Bitwarden doesn't use fields like "assigned", "milestone", or "project" to track progress.