hasValidToken method
Returns true if a non-expired token exists in storage.
Unlike getValidToken, this method never triggers a refresh — it purely inspects the current stored state. Use it for "are we logged in?" checks in UI code where side effects are unwanted.
Does not respect proactiveWindow: a token that is within the proactive
window but not yet expired returns true.
Implementation
Future<bool> hasValidToken() async {
final token = await _storage.read();
if (token == null) return false;
return token.isValid(_clock.now());
}