Document org-level agent pattern and deployment mirror repos

## Description

The manifesto distinguishes repo-level agents from org-level agents that encode enterprise-wide standards. Git-ape doesn't need to build this mechanism — GitHub Copilot already supports org-level custom instructions. What's needed is documentation showing how to structure the org-level pattern for infrastructure governance.

The key concept: a **deployment mirror repo** contains no agents or skills — only deployment artifacts (`.azure/deployments/`, state, metadata). All agent intelligence lives in the org-level `.github` repository and is inherited automatically. The deployment repo is a pure ledger of infrastructure state.

## Scope

1. **Org-level pattern guide** — Document how to set up an organization `.github` repo with:
- `copilot-instructions.md` containing security baselines, naming conventions, approved regions, compliance rules.
- Git-ape agents and skills installed at org level (inherited by all repos).
- Org-level guardrails that repo-level instructions cannot weaken.
2. **Deployment mirror repo guide** — Document the pattern where:
- A repo contains only `.azure/deployments/` with templates, state, metadata, and architecture diagrams.
- No `.github/agents/` or `.github/skills/` — all agent capabilities come from the org-level plugin/repo.
- Workflows (`.github/workflows/`) are the only repo-level config (plan, deploy, destroy).
- The repo is a pure infrastructure state ledger, versioned in Git.
3. **Example repo structure** — Show the minimal deployment mirror repo layout.
4. **Multi-repo governance** — How multiple deployment mirror repos share consistent guardrails from one org-level source.

## Acceptance Criteria

- [ ] Guide documenting org-level agent setup for infrastructure governance.
- [ ] Guide documenting deployment mirror repo pattern (no agents, state only).
- [ ] Example minimal repo structure for a deployment mirror.
- [ ] Explanation of how org-level guardrails flow to deployment repos.