feat: add secure storage to store user key

lib/presentation/secure_storage.dart

@@ -0,0 +1,21 @@
+import 'package:flutter_secure_storage/flutter_secure_storage.dart';
+
+class SecureStorageUtil {
+  static const _storage = FlutterSecureStorage(
+    aOptions: AndroidOptions(
+      encryptedSharedPreferences: true,
+    ),
+  );
+
+  static Future<void> setValue(String key, dynamic value) async {
+    await _storage.write(key: key, value: value);
+  }
+
+  static Future<String?> getValue(String key) async {
+    return await _storage.read(key: key);
+  }
+
+  static Future<void> remove(String key) async {
+    await _storage.delete(key: key);
+  }
+}