Create official GitHub Action for CI/CD integration

[bingenito]

Proposal

Create official GitHub Action for URL detection in CI/CD.

Features

• Automatic PR comments with detected URLs
• Check runs integration
• Diff-only scanning (only changed files)
• Policy enforcement
• Configurable failure thresholds

Files to Create

• action.yml - GitHub Action definition
• .github/workflows/demo.yml - Example workflow
• Documentation for action usage

Example Workflow

- uses: morganstanley/url-detector@v1
  with:
    scan: 'src/**/*.ts'
    fail-on-urls: true
    ignore-domains: '*.example.com'

Priority

Phase 4 - Advanced Features (Lower Priority)

Related to TODO.md section 4.2