Implement user authentication

[shinyay]

Related to #2

Implement user authentication system using GitHub OAuth2.

• OAuth2 Provider Configuration: Update app.py to configure GitHub as the OAuth2 provider with client ID and client secret.
• OAuth2 Flow: Modify app.py to handle GitHub login and registration, including secure user information storage in the database.
• Session Management: Integrate session management functions from session_management.py into app.py.
• Error Handling: Register error handlers from error_handling.py in app.py.
• Login Page: Update templates/login.html to change the login form action to /login/github.
• Unit Tests: Update tests/test_authentication.py to reflect GitHub OAuth2 integration, add tests for session management and error handling functions.
• Documentation: Update README.md to reflect GitHub OAuth2 integration, add instructions for running unit tests for authentication.
• Dependencies: Add werkzeug to the list of dependencies in requirements.txt.

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