Fix professionals list never loading when user has no city

updateCity skipped getProfessionals() when both _city and the incoming
city were null (null != null = false). Added _initialized flag so the
first call always triggers the load regardless of city value.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/providers/professionals_provider.dart

@@ -6,10 +6,13 @@ class ProfessionalsProvider extends ChangeNotifier {
   List<UsuarioProfesional> professionals = [];
   bool isLoading = true;
   String? _city;
+  bool _initialized = false;
   final _api = ApiService.instance;
 
   void updateCity(String? city) {
-    if (_city != city) {
+    // Always load on first auth event; afterwards only reload when city changes.
+    if (!_initialized || _city != city) {
+      _initialized = true;
       _city = city;
       getProfessionals();
     }