Retry GitHub PR metadata reads in shared checks

[gontzess]

Why

Two Axiomatic connector PRs failed required shared checks when workflow-scoped GitHub API reads returned 404 for valid PR metadata endpoints. A same-minute Axiomatic PR passed the same shared workflow commit, and connector verify plus metadata checks passed, so the failure is isolated to PR metadata reads rather than connector code.

This keeps the trust boundary unchanged: the workflows do not fall back to reading additional PR checkout content under elevated permissions.

What this changes

• Adds bounded retries around PR metadata REST and GraphQL reads used by connector docs and PR review checks.
• Retries 408, 429, and 5xx responses through the normal retry window, allows one extra 404 attempt, and fails 403 immediately.
• Adds endpoint, repository, PR number, attempt count, and GitHub request ID where available to final docs-check errors.
• Extends connector docs precheck tests for retry behavior and authorization-style failures.

Validation

• node --test tools/connector-docs/check-docs-change.test.mjs
• python3 -m py_compile .github/actions/pr-review/scripts/fetch-pr-context.py .github/actions/pr-review/scripts/resolve-outdated-threads.py
• git diff --check

Draft until the affected connector PR checks can be rerun against this workflow change.