Deployment Ready: Fixed scam detection low confidence, added production audit report, optimized throttles

feat(ui): update landing page with Sentinel branding and docs links

✨ UI: Enhanced stat cards with 3D icons, depth shadows, and mobile responsiveness

📄 UI: Added GUVI Challenge endpoint to landing page API reference

🚀 DEPLOY: Restored dynamic placeholders in the new Ultra-Premium landing page

📦 REFACTOR: Moved HTML landing page to app/templates/index.html