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/Calendar/CalendarHostView.swift

@@ -95,6 +95,9 @@ struct CalendarHostView: View {
         .onReceive(NotificationCenter.default.publisher(for: .manualSyncRequested)) { _ in
             Task { await forceReload() }
         }
+        .onReceive(NotificationCenter.default.publisher(for: .rescheduleReminders)) { _ in
+            store.rescheduleNotifications()
+        }
     }
 
     // MARK: – Liquid Glass variant
@@ -162,6 +165,9 @@ struct CalendarHostView: View {
         .onReceive(NotificationCenter.default.publisher(for: .manualSyncRequested)) { _ in
             Task { await forceReload() }
         }
+        .onReceive(NotificationCenter.default.publisher(for: .rescheduleReminders)) { _ in
+            store.rescheduleNotifications()
+        }
     }
 
     // MARK: – Top bar (flat mode)
@@ -407,6 +413,8 @@ struct CalendarHostView: View {
     // MARK: – Loading logic
 
     private func startup() async {
+        // Ask for notification permission early so reminders can be scheduled.
+        NotificationScheduler.requestAuthorizationIfNeeded()
         // 0. Pull settings first so week-start / default-view are correct
         //    before we compute the initial range and load events.
         await SettingsSync.pull(api: api)