feat: add red team security auditor agentic workflow (#170)

Adds a GitHub Agentic Workflow (gh-aw) that performs CTF-style security
audits of the ado-aw codebase every 2 days (~3 times/week).

The agent round-robins through six vulnerability categories:
- Input sanitization & injection (template, YAML, shell, VSO)
- Path traversal & file system escape
- Network & domain allowlist bypass
- Credential & secret exposure
- Logic & authorization flaws
- Supply chain & dependency integrity

Uses cache-memory to track progress across runs and avoid duplicate
reports. Creates a single consolidated GitHub issue per run when
exploitable vulnerabilities are found.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jamesadevine