Validate the current user's stored openEO credentials against the backend.

Makes a live request to the configured openEO backend.

Authentication: JWT token required.

Response Schema::

{
  "data": {
    "valid": true,
    "message": "Credentials are valid"
  }
}

Error Responses:

• 401 Unauthorized
• 404 Not Found: user not found
• 500 Internal Server Error