[Bug] /api/v1/users/me returns display_name: null for Apple ID login accounts

[wanghuan-520]

Summary

For Apple ID login accounts, /api/v1/users/me returns display_name: null, which causes the NyxID App User page to show Display Name: Not set.

Actual

GET /api/v1/users/me returns:

{
  "display_name": null
}

The app displays:

• Display Name: Not set

Expected

If Apple provides the user's name during first authorization, NyxID should persist it and return the correct display_name from /api/v1/users/me.

If Apple does not provide a name in this flow, that behavior should be clearly defined and the UI should avoid showing a confusing result.

Impact

• Apple ID users see incomplete profile information
• It is unclear whether this is expected Apple behavior or a backend persistence issue
• The current UI makes the account look broken

Notes

This appears to be backend-side first, since the frontend is rendering the null value returned by /api/v1/users/me.

Need to verify:

• whether Apple name data is received during first authorization
• whether display_name is persisted correctly in the Apple login flow