Security & HF Spaces fixes: Enable CSRF, auth middleware, persistent storage

Fix: Auth status endpoint response format and frontend cache

Fix: Correct OAuth callback URL path mismatch

Fix: Add /oauth-callback endpoint for OAuth flow

Fix: Add backend OAuth config API for client_id

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Fix HF Spaces iframe session persistence with localStorage fallback

Implement HF Spaces best practice: new tab login flow

Add debug logging to auth status endpoint

Simplify authentication flow to fix login issues

Fix login modal authentication issues

Separate login page to HTML template for better maintainability

Use shadcn/ui design system for login page consistency

✨ Simplify landing page: Bigger CTA & cleaner design

🎨 Complete redesign: Premium research platform landing page

Redesign login page with cleaner, minimal design

Remove target='_blank' for single-page login experience

Fix iframe cookie issues for HF Spaces

Fix OAuth according to HF official documentation

Fix UnboundLocalError and add environment detection debug

Add comprehensive session debugging

Fix HF user info parsing and OAuth scope issues

Fix session persistence and add detailed debugging

Fix OAuth state verification and permissions policy issues

Fix OAuth redirect URI for HF Spaces

Fix middleware order and session access issues

Implement mandatory authentication and usage tracking for OpenAI API protection

Fix HF Spaces authentication: support __sign parameter and make auth optional

Implement conditional authentication middleware and OAuth routes for Hugging Face Spaces integration. Enhance environment debugging and add environment info endpoint. Update README with OAuth configuration details and improve startup logging.