Add meaningful tests for workflow scripts

[jdelfino]

Context

Depends on #37 (shared libs) and #38 (script extraction).

Current tests (3 .py + 2 .sh files) are keyword-grep checks against inline YAML — they validate almost nothing. With scripts extracted into standalone JS modules, we can write real unit tests.

Task

Language: Node.js (using built-in node:test runner, Node 18+)

1. YAML structure validation (tests/validate-workflows.js)

• Parse each .yml with js-yaml
• Validate: name, triggers, permissions, job structure, job dependencies
• Replaces all existing structural tests

2. Unit tests for lib modules (tests/lib/*.test.js)

Test pure logic with real inputs — no GitHub API mocking:

Test file	What's tested
config.test.js	YAML section parsing with various inputs
file-patterns.test.js	Test/code/dependency file detection edge cases
commit-validator.test.js	Conventional commit format validation
scope-matcher.test.js	File path extraction from markdown + scope matching
api-patterns.test.js	Language-specific API surface regex patterns
patch-parser.test.js	Unified diff line number tracking
severity.test.js	Review comment severity keyword detection
approval.test.js	Non-stale approval logic
fixes-parser.test.js	Fixes #N extraction from PR bodies
pr-body.test.js	Idempotent section replacement

3. Delete old tests

• tests/test_guardrail_test_ratio.py
• tests/test_human_review_workflow.py
• tests/test_pr_review_workflow.py
• tests/test-guardrail-commits.sh
• tests/test-guardrail-scope.sh

Files

• tests/validate-workflows.js (new)
• tests/lib/*.test.js (10 new files)
• tests/*.py, tests/*.sh (5 deleted)