Issue Description

The repository needs custom chat mode configuration files for GitHub Copilot to provide specialized assistance for different development scenarios.

Additional Context

Files to add:

• .github/copilot/chatmodes/markdown-expert.chatmode.md - Markdown authoring specialist
• .github/copilot/chatmodes/powershell-expert.chatmode.md - PowerShell development specialist
• .github/copilot/chatmodes/workflow-expert.chatmode.md - GitHub Actions workflow specialist
• .github/copilot/chatmodes/security-expert.chatmode.md - Security and compliance specialist
• .github/copilot/chatmodes/testing-expert.chatmode.md - Testing and validation specialist

Priority: Wave 1 (Priority 1) - Can merge in parallel with other Wave 1 PRs

Dependencies: None - independent issue

Testing: Validate markdown syntax, verify chatmode files are recognized by Copilot, test each chatmode's specialized prompting