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

Workouts/Views/Today/ScheduleAddEditView.swift

@@ -8,6 +8,7 @@
 import IndieSync
 import SwiftUI
 import SwiftData
+import UserNotifications
 
 /// The UI-only "When" choice — a superset of `ScheduleRecurrence` with one extra
 /// option, `.now`, that never gets persisted: it skips the schedule document
@@ -68,6 +69,12 @@ struct ScheduleAddEditView: View {
     @State private var when: WhenChoice
     @State private var weekdays: Set<Int>
     @State private var date: Date
+    @State private var reminderEnabled: Bool
+    @State private var reminderTime: Date
+    /// Notification permission has been explicitly denied — surfaced as a footer so
+    /// the user knows reminders won't arrive until re-enabled in Settings. Checked
+    /// async on appear; never blocks the form.
+    @State private var notificationsDenied = false
 
     /// "Now" starts a workout immediately instead of saving a schedule — only offered
     /// when adding (not editing) for today's default date, since a past/future day
@@ -95,6 +102,8 @@ struct ScheduleAddEditView: View {
         _goal = State(initialValue: schedule?.goalKind)
         _weekdays = State(initialValue: Set(schedule?.weekdays ?? []))
         _date = State(initialValue: schedule?.date ?? defaultDate)
+        _reminderEnabled = State(initialValue: schedule?.reminderMinutes != nil)
+        _reminderTime = State(initialValue: Self.time(fromMinutes: schedule?.reminderMinutes))
         self.onStartNow = onStartNow
 
         let offersNow = schedule == nil && defaultDate.isSameDay(as: Date())
@@ -131,6 +140,7 @@ struct ScheduleAddEditView: View {
                 routineSection
                 if when != .now {
                     goalSection
+                    reminderSection
                 }
             }
             .navigationTitle(isEditing ? "Edit Workout" : "New Workout")
@@ -148,6 +158,11 @@ struct ScheduleAddEditView: View {
                 // Default to the first routine when adding (the @Query isn't populated at init).
                 if routineID.isEmpty { routineID = routines.first?.id ?? "" }
             }
+            .task {
+                // Surface a denied permission as a footer note — informational only.
+                let settings = await UNUserNotificationCenter.current().notificationSettings()
+                notificationsDenied = settings.authorizationStatus == .denied
+            }
         }
     }
 
@@ -221,6 +236,21 @@ struct ScheduleAddEditView: View {
         }
     }
 
+    private var reminderSection: some View {
+        Section {
+            Toggle("Remind Me", isOn: $reminderEnabled)
+            if reminderEnabled {
+                DatePicker("Time", selection: $reminderTime, displayedComponents: .hourAndMinute)
+            }
+        } header: {
+            Text("Reminder")
+        } footer: {
+            if reminderEnabled && notificationsDenied {
+                Text("Notifications are turned off for Workouts. Reminders won't arrive until you enable them in Settings.")
+            }
+        }
+    }
+
     /// A row of toggleable weekday chips, Monday-first.
     private var weekdayPicker: some View {
         HStack(spacing: 6) {
@@ -264,6 +294,7 @@ struct ScheduleAddEditView: View {
             recurrence: recurrence.rawValue,
             weekdays: recurrence == .fixedDays ? weekdays.sorted() : nil,
             date: recurrence == .once ? date : nil,
+            reminderMinutes: reminderEnabled ? Self.minutesFromMidnight(of: reminderTime) : nil,
             order: isEditing ? order : nextOrder(),
             createdAt: createdAt,
             updatedAt: Date()
@@ -277,6 +308,22 @@ struct ScheduleAddEditView: View {
         let existing = (try? modelContext.fetch(FetchDescriptor<Schedule>())) ?? []
         return (existing.map(\.order).max() ?? -1) + 1
     }
+
+    // MARK: - Reminder time conversion
+
+    /// A Date (today, local calendar) at the stored minutes-from-midnight, for the
+    /// hour-and-minute picker. Nil (no reminder yet) seeds a sensible 8:00 AM default.
+    private static func time(fromMinutes minutes: Int?) -> Date {
+        let startOfDay = Calendar.current.startOfDay(for: Date())
+        return Calendar.current.date(byAdding: .minute, value: minutes ?? 8 * 60, to: startOfDay)
+            ?? startOfDay
+    }
+
+    /// The picked time back to minutes from midnight (local wall-clock).
+    private static func minutesFromMidnight(of time: Date) -> Int {
+        let comps = Calendar.current.dateComponents([.hour, .minute], from: time)
+        return (comps.hour ?? 0) * 60 + (comps.minute ?? 0)
+    }
 }
 
 // MARK: - Routine picker