- Update all un.* implementations to use HMAC-SHA256 signing
- Headers: Authorization (Bearer public_key), X-Timestamp, X-Signature
- Signature: HMAC-SHA256(secret_key, "timestamp:METHOD:path:body")
- Fix test suite issues (bash arithmetic, ES module compat, TCL shebang)
- Add CLAUDE.md with inception testing documentation
- Update README.md with HMAC auth and dependency table
- All 38 implementations pass inception test via un2