[FEATURE] Add user authentication system

[sbusso]

User Story

As a user, I want to be able to securely authenticate and access my account so that I can use personalized features and protect my data.

Acceptance Criteria

• Users can register for a new account with email and password
• Users can log in with their credentials
• Users can log out from their account
• Passwords are securely hashed and stored
• Authentication state is properly managed across sessions
• Password reset functionality is available
• Input validation for email format and password strength
• Rate limiting for authentication attempts
• User session management and timeout handling

Technical Requirements

• Implement secure password hashing (bcrypt or similar)
• JWT-based session management
• Database schema for user accounts
• Authentication middleware for protected routes
• Frontend authentication forms with proper validation
• Password reset via email verification
• Security headers and CSRF protection
• Unit and integration tests for authentication flows
• API endpoints for authentication operations
• Error handling for authentication failures

Definition of Done

• All acceptance criteria are met
• Code is properly tested with >90% coverage
• Security review completed
• Documentation updated
• Performance meets requirements (<200ms for auth operations)

[sbusso]

✅ Feature broken down into implementation tasks: #6, #7, #8, #9

Task Breakdown:

• [TASK] Backend: Implement user authentication database schema and core API endpoints #6: Backend authentication infrastructure (database schema, API endpoints)
• [TASK] Frontend: Implement authentication forms and user state management #7: Frontend authentication interface (forms, state management)
• [TASK] Security: Implement password reset and security hardening features #8: Security hardening (password reset, rate limiting, CSRF protection)
• [TASK] Testing: Implement comprehensive authentication test suite #9: Comprehensive testing suite (unit, integration, security tests)

Tasks assigned to current iteration and ready for implementation.