chore(mobile): refactor authentication (#14322)

mobile/lib/services/device.service.dart

@@ -0,0 +1,24 @@
+import 'package:flutter_udid/flutter_udid.dart';
+import 'package:hooks_riverpod/hooks_riverpod.dart';
+import 'package:immich_mobile/entities/store.entity.dart';
+
+final deviceServiceProvider = Provider((ref) => DeviceService());
+
+class DeviceService {
+  DeviceService();
+
+  createDeviceId() {
+    return FlutterUdid.consistentUdid;
+  }
+
+  /// Returns the device ID from local storage or creates a new one if not found.
+  ///
+  /// This method first attempts to retrieve the device ID from the local store using
+  /// [StoreKey.deviceId]. If no device ID is found (returns null), it generates a
+  /// new device ID by calling [createDeviceId].
+  ///
+  /// Returns a [String] representing the device's unique identifier.
+  String getDeviceId() {
+    return Store.tryGet(StoreKey.deviceId) ?? createDeviceId();
+  }
+}