feat(calendar): implement ReminderOverlay and supporting components

- Add ReminderQueueManager for managing notification queue
- Add IOSNotificationPayloadBridge for iOS cold start handling
- Add ReminderOverlay UI component with snooze (5/15 min) and complete actions
- Update main.dart to integrate ReminderOverlay
- LocalNotificationService: remove permission fallback logic, add native grouping

apps/lib/core/notifications/ios_notification_payload_bridge.dart

@@ -0,0 +1,27 @@
+import 'dart:convert';
+import 'package:shared_preferences/shared_preferences.dart';
+import '../../features/calendar/reminders/models/reminder_payload.dart';
+
+class IOSNotificationPayloadBridge {
+  static const String _key = 'pending_notification_payload';
+  final SharedPreferences _prefs;
+
+  IOSNotificationPayloadBridge(this._prefs);
+
+  Future<ReminderPayload?> getPendingPayload() async {
+    final raw = _prefs.getString(_key);
+    if (raw == null || raw.isEmpty) {
+      return null;
+    }
+    try {
+      final json = Map<String, dynamic>.from(jsonDecode(raw) as Map);
+      return ReminderPayload.fromJson(json);
+    } catch (_) {
+      return null;
+    }
+  }
+
+  Future<void> clearPendingPayload() async {
+    await _prefs.remove(_key);
+  }
+}