docs(governance): add agent baseline

[TheDanniCraft]

📝 Description

Adds the organization-wide, synchronized AGENTS.md baseline and documents how repositories extend it through an optional AGENTS.local.md.

The baseline links agents to the central Brand repository and its canonical product, design, and generated-asset references. It also records shared Git, pull-request, security, privacy, baseline-sync, and AI-assisted-work rules without imposing Core-specific architecture on every repository. It also protects both global and local agent-guidance files from untrusted pull-request changes.

Refs PAB-52

🧩 Type of Change

• 🧾 Documentation
• 🤖 CI/CD or automation

🗺️ Areas

• Documentation
• Governance
• Infrastructure
• Security

🧪 Testing and Validation

- git diff --check
- node --test .github/scripts/repository-baseline.test.mjs
  15 tests passed

🔐 Security, Compatibility, and Operations

This adds a managed root-level file to the repository baseline. It does not add
credentials, network requests, runtime code, public APIs, or persisted data.
The synchronizer's existing three-way merge behavior applies to the new file.

📋 Checklist

• I have read and understood the Contribution Guidelines
• This pull request addresses one focused change
• My pull-request title follows Conventional Commits
• My commit messages follow Conventional Commits
• I have performed a self-review of the complete diff
• I understand and can explain every submitted change
• I have removed debug output, unrelated changes, and generated noise
• I have added or updated appropriate tests, or explained why none are needed
• I have updated relevant documentation, or explained why none is needed
• My changes introduce no unexpected warnings or errors
• I have considered security, compatibility, deployment, and rollback effects
• I have not included credentials, secrets, private payloads, or personal data
• Any required dependent changes are linked and clearly identified

🤖 AI Usage

• 🤖 This pull request includes AI-assisted work

🛠️ How AI Was Used

• 🧠 Ideation, research, or planning
• 📝 Drafting or editing documentation or other text
• ♻️ Modifying or refactoring code
• 🧪 Designing tests or validation steps

🔎 AI Tools and Human Review

Codex helped plan and apply the documentation and baseline-manifest changes. The
repository owner will review the complete diff, agent instructions, and
synchronization impact before merge.

✅ AI Responsibility

• I reviewed all AI-assisted content line by line
• I verified factual, technical, security, and licensing claims
• I tested the resulting behavior rather than trusting generated assertions
• I accept full responsibility for the submitted work
• I confirm this contribution is not automated spam or generic AI slop

📸 Screenshots, Logs, or Traces

Not applicable.

💬 Additional Context

The follow-up Core PR will add only AGENTS.local.md. It will not alter this
central baseline.

[linear-code]

PAB-52