Write Post 19 (PowerShell Automation Patterns), add architecture diagram

- Post 19: DSC v3 (GA March 2025), PowerShell 7 native Hyper-V module support,
  Get/Test/Set idempotent module pattern, CAF naming standards, centralized
  variables files, SecretManagement, CI/CD pipelines for GitHub/GitLab/Azure DevOps
- Added ps-automation-architecture.svg (4-layer automation framework)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: kristopherjturner