docs: add comprehensive Redis key naming documentation

- Add Redis Key Architecture section to CLAUDE.md
- Document fixed vs rolling window naming conventions
- Explain why fixed mode needs suffix and rolling mode doesn't
- Add detailed examples for all time periods (daily/5h/weekly/monthly)
- Include debugging commands and troubleshooting guide
- Add inline documentation in rate-limit/service.ts
- Benefits: easier debugging, better maintainability, clearer design rationale
- Addresses code review feedback from PR #161