Fix request professional flow for new users

- Add Profesional.empty() factory for users with no professional record
- initState: catch error from getProfessional and show empty form instead of infinite spinner
- Backend upsert: create professional record if none exists (no longer throws 404)

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

lib/models/profesional.dart

@@ -46,6 +46,28 @@ class Profesional {
     required this.paymentMethods,
   });
 
+  static Profesional empty() => Profesional(
+    id: '',
+    identification: '',
+    rethusCode: '',
+    rethusValidated: false,
+    address: '',
+    aditionalAddress: '',
+    profession: '',
+    ratePreferences: false,
+    rate: '',
+    locationPreferences: LocationPreferences.office,
+    bannerPicture: '',
+    identificationPicture: '',
+    certificatePicture: '',
+    latitude: 0.0,
+    longitude: 0.0,
+    specializations: [],
+    specializationsPictures: [],
+    schedules: Schedules.empty,
+    paymentMethods: PaymentMethodEntity.empty,
+  );
+
   static Profesional fromDocument(Map<String, dynamic> doc) {
     // Backend returns schedules as array [{day_of_week, enabled, ...}]; convert to Schedules
     Schedules parsedSchedules = Schedules.empty;