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/calendar_services_provider.dart

@@ -18,6 +18,21 @@ class CalendarServicesProvider extends ChangeNotifier {
     notifyListeners();
   }
 
+  // Returns services for a specific professional via the public endpoint (no auth needed).
+  // Used by CalendarView when a user browses a professional's availability.
+  Future<List<Service>> getPublicServicesForProfessional(String professionalId) async {
+    try {
+      final res = await _api.get('/services/public-calendar/$professionalId');
+      final rawServices = (res as Map<String, dynamic>)['services'] as List? ?? [];
+      return rawServices.map((e) {
+        final m = e as Map<String, dynamic>;
+        return Service.fromJson(m, m['id'] as String);
+      }).toList();
+    } catch (_) {
+      return [];
+    }
+  }
+
   getServicesForProfessional(String userId) async {
     try {
       isLoading = true;