fix: notify immediately when isLoading=true in service fetch methods

Without notifyListeners() after isLoading=true, the Consumer would
briefly show stale data (or 'service not found') from a previous
navigation before the API call completes.

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

lib/providers/services_provider.dart

@@ -66,6 +66,7 @@ class ServicesProvider extends ChangeNotifier {
   getServiceForUser(String serviceId) async {
     try {
       isLoading = true;
+      notifyListeners();
       final data = await _api.get('/services/$serviceId');
       final map = data as Map<String, dynamic>;
       final servicio = Service.fromJson(map, map['id'] as String);
@@ -90,6 +91,7 @@ class ServicesProvider extends ChangeNotifier {
   getServiceForProfessional(String serviceId) async {
     try {
       isLoading = true;
+      notifyListeners();
       final data = await _api.get('/services/$serviceId');
       final map = data as Map<String, dynamic>;
       final servicio = Service.fromJson(map, map['id'] as String);