Add reminder notifications to schedules

- ScheduleDocument/Schedule gain optional reminderMinutes (minutes from
  midnight; decode-compatible, no schema bump)
- New Workout form gets a Reminder section (toggle + time picker, hidden
  for Now; footer warns when notifications are denied)
- ReminderPlanner (pure, tested) derives notification triggers: daily
  repeating, per-weekday repeating for fixed days, one-shot for once
- ReminderScheduler resyncs pending requests from the cache on every
  change, multiplexed onto onCacheChanged after the watch push; asks
  notification permission only once a reminder actually exists

Shared/Model/Mappers.swift

@@ -92,7 +92,7 @@ extension ScheduleDocument {
                   routineID: schedule.routineID, routineName: schedule.routineName,
                   goal: schedule.goalRaw, recurrence: schedule.recurrenceRaw,
                   weekdays: schedule.weekdays,
-                  date: schedule.date,
+                  date: schedule.date, reminderMinutes: schedule.reminderMinutes,
                   order: schedule.order, createdAt: schedule.createdAt, updatedAt: schedule.updatedAt)
     }
 }
@@ -255,7 +255,7 @@ enum CacheMapper {
         } else {
             schedule = Schedule(id: doc.id, routineID: doc.routineID, routineName: doc.routineName,
                                 goalRaw: doc.goal, recurrenceRaw: doc.recurrence, weekdays: doc.weekdays,
-                                date: doc.date, order: doc.order,
+                                date: doc.date, reminderMinutes: doc.reminderMinutes, order: doc.order,
                                 createdAt: doc.createdAt, updatedAt: doc.updatedAt,
                                 jsonRelativePath: relativePath)
             context.insert(schedule)
@@ -266,6 +266,7 @@ enum CacheMapper {
         schedule.recurrenceRaw = doc.recurrence
         schedule.weekdays = doc.weekdays
         schedule.date = doc.date
+        schedule.reminderMinutes = doc.reminderMinutes
         schedule.order = doc.order
         schedule.createdAt = doc.createdAt
         schedule.updatedAt = doc.updatedAt