Polish SEO preview demo experience

[alianjum0]

Summary

• redesign the landing page with a clearer, developer-focused visual language and guided URL input
• add responsive audit summaries, semantic status cards, and realistic social/search previews
• replace the Bootstrap CDN with a local responsive stylesheet and branded missing-image fallback
• remove the portfolio-project label and add technical request/runtime cues
• keep raw Open Graph tag presence separate from preview fallbacks so completeness scoring remains accurate

Tests

• rtk pnpm test (19 passed)
• rtk node --check server.js
• desktop browser validation
• mobile validation at 390x844
• browser console check (no errors)

Review

• reviewed the full diff against current master
• no unrelated or temporary changes found
• existing fetch, SSRF protection, rate limiting, and safe rendering behavior remain covered

Risk

• social previews are approximations and external sites may block automated requests or image hotlinking
• merge does not verify or trigger a production deployment in this workflow