I need a straightforward, secure email-and-password sign-in flow added to my existing Flutter app. No new account creation is required—only pre-existing users should be able to log in—and I’m not interested in Google or Facebook sign-ins for this project. Here’s the flow I’m after: • A clean login screen that validates email format and password length before hitting the backend (use a placeholder API call so I can swap in my real endpoint). • Successful logins route the user to the main screen and keep them signed in between sessions with credentials stored via flutter_secure_storage (Keychain/Keystore on devices). • Failed logins display friendly, localized error messages. • A simple logout button clears the secure store and returns the user to the login screen. Deliverables • Dart code (null-safe) for the UI, state management (Provider, Riverpod or Bloc—your choice), secure credential handling, and an auth service stub. • Clear README with setup steps and where to plug in my actual API. • Brief inline comments so I can maintain the code easily. Once I can drop your files into my project, run flutter pub get, and watch the flow work exactly as above, the job is done.