Add comprehensive Claude Code tooling:
- Agents: docs-researcher, docs-researcher-advanced for documentation research
- Commands: dev:add-e2e-attrs, docs:library, docs:refresh-reference, quality:bundle-analyze, quality:coverage
- Skills: 8 specialized skills including api-change-analyzer, architecture-enforcer, library-scaffolder, and more
Update documentation:
- Comprehensive CLAUDE.md overhaul with library reference system
- Update testing guidelines in docs/guidelines/testing.md
- Update READMEs for checkout, icons, scanner, and scroll-position libraries
Remove outdated checkout-completion-flow-documentation.md
Update .gitignore for Claude Code files