Turn the homepage tamper preview into a prediction challenge

[aruintelligence]

What changed

• Ask visitors to choose a controlled mutation and predict which of three checks fails before revealing the result.
• Reset the answer when the mutation changes, and keep the exact checker deep link for local verification.
• Mirror the homepage source in docs/ for Pages.

Verification

• Inline scripts parse and 36 HTML IDs are unique.
• node --test test/*.test.js (9/9 test files passed).
• Live interaction and visual check after Pages deployment.