fix: credential list now reflects changes immediately

[forkline-bot]

Summary

• Enable soft-fido2's built-in credential management by setting cred_mgmt to Some(true) in the authenticator config
• Remove the custom 0x0a command handler that returned hardcoded responses
• The built-in implementation properly calls AuthenticatorCallbacks methods (enumerate_rps, list_credentials, etc.) which read from the actual storage backend

Problem

When credentials (passkeys) were added, updated, or removed while the passless service was running, the changes were not reflected in passless client list. The updated state only became visible after restarting the passless process.

Root Cause

The custom credential management command handler (0x0a) was returning hardcoded responses instead of querying the actual storage backend. This was because:

1. cred_mgmt was set to None in the authenticator config, disabling soft-fido2's built-in credential management
2. A custom handler was registered for command 0x0a that returned hardcoded test data

Solution

• Enable soft-fido2's built-in credential management by setting cred_mgmt: Some(true)
• Remove the custom 0x0a handler so the built-in implementation handles credential management commands
• The built-in implementation calls PasslessCallbacks::enumerate_rps() and PasslessCallbacks::list_credentials(), which properly read from the storage backend

Testing

The changes ensure that passless client list now reflects credential changes immediately without requiring a restart.

Resolves: #148