docs(integrations): add GitHub Actions runner guide

[jimyag]

Summary

Add a bilingual integration guide for deploying ephemeral GitHub Actions self-hosted runners on Cube Sandbox using jimyag/e2b-github-runner.

Key Changes

• Add English and Chinese integration docs for the GitHub Actions runner deployment flow.
• Document CubeAPI/E2B-compatible configuration, GitHub token permissions, webhook setup, workflow labels, and troubleshooting steps.
• Add the new guide to both integration index pages.

Testing

• npm ci
• npm run docs:build

Notes

• Related to [good first issue] docs: Help us build the use cases #243.
• https://github.com/jimyag/template-repository/pull/1/changes
• https://github.com/jimyag/template-repository/actions/runs/26038198284

[fslongjin]

Nice job! Thanks for your contribution. I have a small question though — in the run logs of your example, I don't seem to see the output from the lines executed in this workflow:

https://github.com/jimyag/template-repository/pull/1/changes#diff-245392b692a50c38ecab4381b118862db514035c10983f3bd4f4b7f1f4be4692R10

This is important for verifying that the GitHub Action was actually running inside CubeSandbox. Could you provide more details on this?