🔑 Implement Authentication (Email/Password + OAuth Google & GitHub) #4

We need to implement a secure and flexible authentication system for Code Showcase Studio.
This will allow users to sign up, log in, and manage sessions using both traditional email/password and OAuth providers (Google & GitHub).

✅ Tasks

• Setup authentication framework
• Email/Password authentication with secure hashing (bcrypt/argon2).
• OAuth integration:
  • Google
  • GitHub
• Session management (JWT or database session).
• Role-based access.
• Profile linking between OAuth accounts and local accounts.
• Add frontend UI for login, signup, and logout.
• Add error handling & validation for auth forms.

🔒 Acceptance Criteria

• Users can register and log in with email & password.
• Users can log in using Google or GitHub.
• System securely handles sessions & tokens.
• Roles (Author, Moderator) are persisted and respected in auth flow.
• OAuth users can still edit their profile.
• Passing tests for all major auth scenarios.