- Create core/oauth module with OAuthProvider enum and shared types
- Implement providers.rs with auth URLs, token exchange, user info endpoints
- Add routes for /auth/oauth/providers, /auth/oauth/{provider}, and callbacks
- Update login.html with OAuth button grid and dynamic provider loading
- Add OAuth config settings to config.csv with setup documentation and links
- Uses HTMX for login form, minimal JS for OAuth provider visibility
