[W-11] Harden the GitHub REST client

[EmersonBraun]

What

Route both GitHub review-state and SCM requests through one internal REST client with consistent API/auth headers, bounded JSON reads, same-origin redirects, Link pagination, and rate-limit handling.

Why

GitHub pagination and primary/secondary rate limits were handled differently between the two modules, and list calls could silently stop at the first page. The request path now honors Retry-After and x-ratelimit-reset for rate-limited GETs while keeping writes single-attempt.

How

• Add the internal src/github-api-client.ts helper and use @agentskit/net 0.2.2 retry and bounded-read primitives.
• Follow same-origin Link: rel="next" links for pull requests, file lists, comments, reviews, check runs, and commit statuses, with existing safety caps preserved.
• Add real localhost node:http coverage for three-page pagination, 429 and secondary 403 recovery, primary reset handling, no POST retry, oversized bodies, and redirects.
• Refresh generated Doc Bridge and README freshness metadata.

Reuse

Published @agentskit/net 0.2.2 provides fetchWithRetry, retry, parseRetryAfter, and readJson; @agentskit/integrations 0.8.1 has GitHub service descriptors and generic HTTP projection, but no GitHub-specific REST client. The shared primitives cover this change, so no Octokit dependency is needed.

Validation

• npm ci and npm ci --prefix apps/docs
• npm run check — passed; 327 tests and all configured docs, public API snapshot, CLI help, and README gates passed.
• npm pack --dry-run — passed.
• git diff --check — passed.
• Public API snapshot unchanged.