[Docs]: add CI Failures troubleshooting guide for contributors

[lishunyang12]

• Populated the empty docs/contributing/ci/failures.md stub with a guide for diagnosing and resolving
  CI failures on PRs
  • Covers all 5 CI checks (pre-commit, Build Wheel, DCO, Read the Docs, Buildkite) with platform info and fix commands
  • Includes a step-by-step workflow: identify the check, check for known issues, investigate locally, file an issue or
    fix it
  • Adds a quick-reference table for common failure patterns (ruff errors, DCO, MkDocs, OOM, timeouts, agent lost, etc.)
  • Cross-links to sibling docs (Markers for Tests, Test File Structure)

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 90d780a1b5

ℹ️ About Codex in GitHub

Codex has been enabled to automatically review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

When you sign up for Codex through ChatGPT, Codex can also answer questions or update the PR, like "@codex address that feedback".

[chatgpt-codex-connector]

Correct Build Wheel trigger description

This row says Build Wheel is one of the checks that run automatically on PRs, but the workflow currently skips docs/markdown-only changes via paths-ignore in .github/workflows/build_wheel.yml (pull request trigger lines 20-26), so contributors following this guide can be confused when the check never appears for documentation PRs. Please clarify that Build Wheel is conditional on changed paths rather than always present.

Useful? React with 👍 / 👎.

[lishunyang12]

Solved.