🔧 Pin minitest to version 5.x and update test stubs for webhook tests

Pin minitest to version 5.27.0 in the Gemfile to retain mock functionality. Update test files to include webmock for stubbing external API requests in webhook tests, ensuring consistent test behavior. ✨ Add QR code generation feature Implement QR code generation endpoints and integrate with the existing API. Update routes, OpenAPI documentation, and add necessary gems for QR code functionality. Enhance service request handling and response formatting for better user experience.