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/models/service.dart

@@ -113,8 +113,10 @@ class Service {
   static TimeOfDay parseTimeOfDay(String timeString) => _parseTime(timeString);
 
   String? formatTimeOfDay(TimeOfDay? time) {
-    if (time != null) return '${time.hour}:${time.minute}';
-    return null;
+    if (time == null) return null;
+    final h = time.hour.toString().padLeft(2, '0');
+    final m = time.minute.toString().padLeft(2, '0');
+    return '$h:$m';
   }
 
   @override