Add dedicated unit tests for getForwardedClientIp

[ryota-murakami]

Summary

getForwardedClientIp lacks dedicated unit tests.

Source

P2 follow-up from /ship adversarial review of PR #176 (silent GitHub token refresh).

Details

Need coverage for multi-hop chain, whitespace, empty header, and malformed input.

Acceptance

• Test file src/tests/unit/lib/utils/get-client-ip.test.ts created
• Coverage: multi-hop chain, whitespace handling, empty header, malformed input, missing header