fix(agenda): one slot generator for professional and patient

The two calendars each built their own list of hours. The patient's
enforced a 3-hour booking lead time; the professional's did not, so at
15:00 an 08:00-18:00 agenda reported "3 libres" (15, 16, 17) that no
patient could actually take.

Both now go through SlotGenerator. The professional still sees the
near-term hours (blocking the next hour is legitimate) but they are
labelled "Sin reserva" and excluded from the "libres" count, so the
number on his agenda means what the patient sees.

Also in this pass:

- endOf() clamps the slot end at 23:59; a 120-minute slot booked at
  23:00 was sending "25:00" to the backend.
- ScheduleEntity.copyWith can set an hour back to null, so returning a
  day to jornada continua no longer keeps the split hours around.
- Removed the Firebase-era schedule map ('habilitado', 'range1Hour1')
  together with the dead ProfessionalEntity.fromDocument that fed it.
- Settings loads guard on mounted and swallow failures instead of
  calling setState after dispose.
- "Pedir cita" says what is missing instead of doing nothing.

Tests: 9 passing, including the clamp and the empty/inverted ranges.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

lib/utils/schedule_validation.dart

@@ -0,0 +1,64 @@
+import 'package:professional_repository/professional_repository.dart';
+import 'package:prosappco/utils/time_of_day_extension.dart';
+
+const _dayNames = [
+  'Lunes',
+  'Martes',
+  'Miércoles',
+  'Jueves',
+  'Viernes',
+  'Sábado',
+  'Domingo',
+];
+
+/// Human-readable problems with a week of opening hours, empty when it is fine.
+///
+/// Nothing validated these before: an inverted or half-filled day saved
+/// happily and then produced zero bookable slots, with no clue as to why.
+List<String> validateSchedules(Schedules schedules) {
+  final days = [
+    schedules.monday,
+    schedules.tuesday,
+    schedules.wednesday,
+    schedules.thursday,
+    schedules.friday,
+    schedules.saturday,
+    schedules.sunday,
+  ];
+
+  final problems = <String>[];
+  for (var i = 0; i < days.length; i++) {
+    final problem = _validateDay(days[i]);
+    if (problem != null) problems.add('${_dayNames[i]}: $problem');
+  }
+  return problems;
+}
+
+String? _validateDay(ScheduleEntity day) {
+  if (!day.enabled) return null;
+
+  if (day.continuousDay) {
+    if (day.range1Hour1 == null || day.range2Hour2 == null) {
+      return 'falta la hora de apertura o de cierre';
+    }
+    if (!day.range1Hour1!.isBefore(day.range2Hour2!)) {
+      return 'la hora de cierre debe ser posterior a la de apertura';
+    }
+    return null;
+  }
+
+  final r = [day.range1Hour1, day.range1Hour2, day.range2Hour1, day.range2Hour2];
+  if (r.any((t) => t == null)) {
+    return 'faltan horas en la jornada partida';
+  }
+  if (!r[0]!.isBefore(r[1]!)) {
+    return 'la primera jornada termina antes de empezar';
+  }
+  if (!r[2]!.isBefore(r[3]!)) {
+    return 'la segunda jornada termina antes de empezar';
+  }
+  if (r[2]!.isBefore(r[1]!)) {
+    return 'las dos jornadas se cruzan';
+  }
+  return null;
+}