fix(scheduling): fix schedule save endpoint, time format, and calendar load

Critical fixes for the scheduling flow:

- ScheduleEntity: add toScheduleDto() with snake_case keys, day_of_week,
  and HH:MM zero-padded format required by the backend DTO @Matches validator
- Schedules: add toSchedulesArray() converting the day-keyed object to the
  array format expected by PATCH /professionals/me/schedules
- ProfessionalFormProvider: updateProfesionalProfileScheduleInfo now calls
  the correct endpoint (/professionals/me/schedules) instead of /professionals/me
  which was stripping the schedules field via ValidationPipe whitelist
- Service.formatTimeOfDay: zero-pad hours and minutes so POST /services passes
  the @Matches(/^\d{2}:\d{2}$/) DTO validation
- ProfessionalProvider: add getProfessionalById() calling /professionals/:id
  (public endpoint) to load any professional's data, not the viewer's own
- CalendarServicesProvider: add getPublicServicesForProfessional() calling
  /services/public-calendar/:id so the user calendar shows the target
  professional's booked slots, not the viewer's own services
- CalendarView: use getProfessionalById + getPublicServicesForProfessional
  so the calendar correctly reflects the selected professional's schedule

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

lib/providers/professional_form_provider.dart

@@ -106,12 +106,14 @@ class ProfessionalFormProvider with ChangeNotifier {
 
   Future<bool> updateProfesionalProfileScheduleInfo(String userId) async {
     try {
-      await _api.patch('/professionals/me', profesional!.toDocument());
+      await _api.patch('/professionals/me/schedules', {
+        'schedules': profesional!.schedules.toSchedulesArray(),
+      });
     } catch (e) {
       NotificationsService.showSnackbar('Error al guardar: $e');
       return false;
     }
-    NotificationsService.showSnackbar('Información actualizada');
+    NotificationsService.showSnackbar('Horario actualizado');
     return true;
   }