feat(percy): full-parity clone with all widths, browsers, and exact names

Rewrite screenshot clone to use direct tile API instead of percy upload.
percy upload creates flat snapshots (one per image), losing the
multi-width/multi-browser structure.

New approach preserves 100% source parity:
- Exact snapshot names from source
- All width variants per snapshot (375, 768, 1080, 1170, 1280px etc)
- All browser comparisons (Chrome, Firefox, Safari, Edge etc)
- Real device/OS info copied from source comparison tags
- Rate limiting protection (200ms delay between API calls)
- Strict base64 for tile uploads (no padding)

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

Author: DeRaowl