Write test-to-code ratio guardrail

[jdelfino]

Write the test-to-code ratio guardrail check.

File

.github/workflows/guardrail-test-ratio.yml

What

• Trigger: PR opened or synchronized
• Calculate ratio of test lines to implementation lines in PR diff
• Test files identified by naming convention (test, spec, tests/)
• Configurable threshold from config.yaml (default: 0.5)
• Below threshold: action_required; above: success
• Check for non-stale PR approval override

Reference

• docs/design.md: Test-to-Code Ratio (Layer 4)