Issue Description

The repository needs PowerShell scripts for security scanning, including SHA pinning validation, staleness checking, and automated updates for GitHub Actions.

Additional Context

Files to add:

• scripts/security/Test-DependencyPinning.ps1 - Validate dependencies are pinned to SHAs
• scripts/security/Test-SHAStaleness.ps1 - Check for stale SHA references
• scripts/security/Update-ActionSHAPinning.ps1 - Update action references to latest SHAs

Priority: Wave 2 (Priority 2) - Depends on Wave 1 completion

Dependencies: Requires scripts/README.md from repository foundation issue

Testing: Execute each script, verify JSON output format, test with sample workflow files