Flutter Email Login Integration

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.