Build a fully responsive dark-themed authentication system using Flutter for a mobile application, following BLoC (Business Logic Component) architecture for clean separation of UI and logic. The app should communicate with a separate backend, and all API calls must be handled through a dedicated service module.

Pages/Components: Login Page

Signup/Register Page

OTP Verification Page (for confirming email/phone during signup or password reset)

Forgot Password Page

Reset Password Page

Features: Sleek and modern dark theme UI using Flutter's ThemeData.dark()

Form validation (email, password, OTP) using Form & TextFormField validators

Password visibility toggle using ObscureText flags

Error/success message display using SnackBars, dialogs, or banners

Loading indicators (e.g., CircularProgressIndicator) during network calls

API Integration: Do not use Firebase for email/password login

Social login (Google, Facebook, Twitter) should be supported using OAuth tokens handled by the backend

Create a separate services module to handle all API calls with a centralized HTTP client (e.g., using the http or Dio package):

Login

Register

Send/verify OTP

Forgot password

Reset password

Social login (OAuth)

Implement global error handling and token management

Social Authentication: Integrate Google, Facebook, and Twitter OAuth via Flutter packages (e.g., google_sign_in, flutter_facebook_auth, twitter_login)

Obtain user credentials via plugins, send tokens to the backend for authentication

State Management: Use Flutter BLoC (flutter_bloc package) to manage state across all authentication flows

Separate logic into Events, States, and Blocs for each screen (e.g., LoginBloc, RegisterBloc)

Routing: Use Navigator 2.0 or GoRouter for handling navigation between pages

Responsiveness: Ensure all pages are fully responsive and adaptive to multiple screen sizes (phones, tablets)

Optional Enhancements: Dark mode toggle (default is dark theme)

Add unit and widget tests for form logic and BLoC states

Implement a “Remember Me” feature using flutter_secure_storage