Make tamper probes interactive and shareable

[aruintelligence]

What changed

• Add a two-choice tamper preview to the homepage that updates the predicted failing check and opens the exact checker probe.
• Allow example=challenge&probe=gate|source deep links that rebuild the changed example locally, with a copy link control.
• Strip the example query when a visitor edits or loads their own record, so its URL does not misrepresent private input.

Verification

• node --check docs/check-run.js
• node --test test/*.test.js (9/9 files passed)
• Live homepage and checker inspection after Pages deploy.