ci: enable locked checkout cache

[dongkeren]

Summary

• pass Buildchain locked source checkout cache inputs to Build and Release - Verify
• document the checkout cache and Node source mirror variables
• set repo variables for the local HTTP mirror path used by self-hosted runners

Verification

• python YAML parse for workflow files
• pnpm exec prettier --check README.md .github/workflows/build.yml .github/workflows/release-verify.yaml
• git diff --check
• git ls-remote against local HTTP mirrors for libnode and node tag

[kungfu-origin]

Approved for workflow cache integration.