Make the saved-run challenge one click from home

[aruintelligence]

What changed

• Route all three homepage challenge entries to a captured example that loads and rechecks automatically.
• Move the change/restore action immediately under the checker verdict and make its stage and changed claim explicit.
• Scroll and focus the challenge after loading, so narrow-screen visitors reach the result without passing the JSON editor.
• Keep the general local-file checker path and its unsigned self-check limitations intact.

Verification

• node --test test/*.test.js (9 test files passed)
• node --check docs/check-run.js
• HTML IDs unique; three homepage challenge links point to the focused route; root/docs homepage copies match.