Improve demo site readability and UX

[okasi]

Summary

Redesigns the GitHub Pages live demo (docs/) for much better readability and clearer interaction flow.

Layout & typography

• Light/dark responsive theme with 17px base font and improved contrast
• Summary bar at the top: instant verdict, behavioral verdict, install snippet
• Skip link and mobile-friendly stacked layout

Instant detection panel

• Verdict card with icon, status text, and pill badge
• Three-column flags table: Flag | What it checks | Status
• Filter chips: All / Triggered / Clear, with empty-state message
• Zebra striping for easier row scanning

Behavioral detection panel

• Score bar with 0.55 threshold marker and legend
• Numbered interaction steps in a dashed “try it yourself” zone
• Signal cards now show human-readable descriptions (not just IDs)
• Simulate webdriver / Playwright buttons for quick testing

Other

• Copy button for npm install detect-bot-client

Test plan

• npm run build:site succeeds
• Open docs/index.html locally (or after Pages deploy) and verify instant checks run on load
• Filter chips show/hide rows correctly
• Behavioral observe flow updates score bar and signal cards
• Copy install button works over HTTPS (GitHub Pages)