Issue Description

Apply ConvertTo-GitHubActionsEscaped from CIHelpers module to security validation scripts that emit workflow commands. This prevents workflow command injection when user-controlled data (file paths, SHA values, action names) appears in CI output.

Files to update:

• scripts/security/Test-DependencyPinning.ps1
• scripts/security/Test-SHAStaleness.ps1
• scripts/security/Update-ActionSHAPinning.ps1

Additional Context

Related to PR #354 which introduced the CIHelpers module with escape functions. Security scripts are particularly important to harden since they process external data from GitHub Actions definitions.