feat: event reminders + default reminder setting + local notifications (iOS)

Per-event reminders (multiple, local calendars only) in the editor, prefilled
from a new "default reminder" setting that applies to all events otherwise.
CalEvent gains `reminders`; AppSettings/SettingsSync sync default_reminder_minutes
(always group). New NotificationScheduler requests permission and schedules the
soonest ≤60 upcoming reminders via UNUserNotificationCenter, rescheduling on
load/sync/edit and when the default changes (skipped in group overlay).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Calendarr iOS/Views/SettingsView.swift

@@ -22,6 +22,7 @@ struct SettingsView: View {
     @AppStorage("defaultView")       private var defaultView = "month"
     @AppStorage("weekStartDay")      private var weekStartDay = "monday"
     @AppStorage("dimPastEvents")     private var dimPastEvents = false
+    @AppStorage("defaultReminderMinutes") private var defaultReminderMinutes = -1
 
     // Profile chapter (server-backed; loaded on appear).
     @State private var displayName = ""
@@ -37,6 +38,7 @@ struct SettingsView: View {
             Form {
                 profilSection
                 privatsphaereSection
+                benachrichtigungenSection
                 geteilterKalenderSection
                 liquidGlassSection
                 cacheSection
@@ -105,6 +107,27 @@ struct SettingsView: View {
         }
     }
 
+    // MARK: – Benachrichtigungen
+
+    var benachrichtigungenSection: some View {
+        Section {
+            Picker(ReminderOptions.defaultTitle(appLang), selection: $defaultReminderMinutes) {
+                Text(ReminderOptions.off(appLang)).tag(-1)
+                ForEach(ReminderOptions.all, id: \.self) { m in
+                    Text(ReminderOptions.label(m, appLang)).tag(m)
+                }
+            }
+            .onChange(of: defaultReminderMinutes) { _, _ in
+                SettingsSync.push(api: api)
+                NotificationCenter.default.post(name: .rescheduleReminders, object: nil)
+            }
+        } header: {
+            Text(ReminderOptions.sectionTitle(appLang))
+        } footer: {
+            Text(ReminderOptions.defaultFooter(appLang)).font(.caption)
+        }
+    }
+
     // MARK: – Privatsphäre
 
     var privatsphaereSection: some View {