- Add reusable header components (X-RateLimit-Limit, X-RateLimit-Remaining, X-RateLimit-Reset, Retry-After)
- Reference headers in 200 responses on all conversion and demo endpoints
- Add Retry-After header to 429 responses
- Update Rate Limits section in API description to mention response headers
- Add comprehensive tests for header documentation (21 new tests)
- All 809 tests passing