feat(auth): complete SignIn/SignUp module with validation and state handling
- Implemented SignIn (Login) and SignUp (Registration) flows using MVVM architecture.
- Added AuthState (Idle, Success, Error) for better UI state management.
- Integrated AuthViewModel with UserRepository for authentication logic.
- LoginFragment: • Handles user input validation. • Triggers login process and observes authState. • Navigates to Home on success, shows BottomSheet on error.
- SignupFragment: • Validates input fields (first name, last name, username, password). • Handles new user registration and error cases (duplicate user). • Shows Snackbar feedback and navigates back to Login after success.
- Repository integrated with Room DB for user persistence and session management.
- Applied proper input validation (minimum password length, required fields).
- Improved user feedback with ProgressBar, BottomSheet, and Snackbar.