refactor(percy): rewrite clone as URL replay — uses Percy CLI for full resources

Previous approach: downloaded root HTML only → CSS/JS/images missing → broken rendering.

New approach: URL Replay mode
- Extracts snapshot names/URLs from source build
- If names are URLs: uses Percy CLI to re-snapshot them
  → Percy CLI handles full resource discovery (CSS, JS, images, fonts)
  → All dependencies uploaded with correct SHAs
  → Percy re-renders with complete styling
- If names are not URLs: shows instructions with snapshot list

Fallback: Screenshot Copy mode (for app/screenshot builds)
- Downloads screenshots and re-uploads as tiles
- Same as before but cleaner code

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: DeRaowl