Address review feedback on PR #101:
1. Capture resp.StatusCode and Retry-After header *before* passing resp
to handleResponse, making ownership transfer explicit. Previously the
caller read resp.StatusCode after handleResponse had closed the body —
correct but fragile coupling.
2. Add panic guard ensuring backoff slice length equals maxAttempts-1.
Previously the relationship was implicit and could silently break if
maxAttempts were changed without updating the default backoff.
Add GitHub API client with configurable base URL and GHE support,
HTTP helpers with 429 retry and Retry-After handling.
Also adds Patch field to vcs.ChangedFile.
Part 1 of 3 for #80.
claw
aweiker