fix(agama-flow-passkey): Fix critical passkey usability and data issues in FIDO implementation

Prioritized GitHub Issues for Janssen Passkey Enhancement Spec ([wiki](https://github.com/JanssenProject/jans/wiki/(Draft-proposal):-Janssen-Passkey-Enhancement-Spec)), issue no: 1

**Description:**
This issue covers immediate fixes required to improve production stability and user experience for passkey functionality in Janssen Server.

**Tasks**

- Remove alert() debug statement from passkey-add.ftlh
- Currently visible to end users in production
- Impacts UX and professionalism

- Fix dead code in FidoValidator.assertionRequest()
- content string is constructed but overwritten
- Clean up logic to avoid confusion and potential bugs

- Make nickname optional during passkey registration
- Remove required validation
- Default value:
- Device type (if available), OR
- "My Passkey"
- Improves conversion rate during registration

- Fix filtering in `ScimFido2Helper`
- deviceData entries are being silently dropped
- Platform authenticators (e.g., built-in passkeys) are affected
- Ensure all valid credentials are returned