- Add TESTING_REGLAMENT.md: session separation, checklist, PR report, testing board
- Add TESTING-SKILL.template.md: blank template for new projects
- Update E2E_TESTING_STRATEGY.md: three E2E principles (user actions only,
  full lifecycle, MCP verification rules)
- Update CLAUDE_INSTRUCTIONS.md: rules #6 (no API calls) and #7 (full lifecycle)
  with carousel example
- Update README.md: structure, principles summary, docs table

Based on real testing experience with Design Preview project.

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