docs(repo): align documentation scopes and skill tooling

[specter119]

Description

• Clarify mutually exclusive documentation ownership by fact type across AGENTS.md, README.md, product, reference, design, status, maintenance, roadmap, and milestone records.
• Preserve M3/M4 historical evidence while removing duplicate current-contract and status definitions.
• Add orthogonal scope boundaries and Good/Bad patterns to the six Luwu review skills.
• Add pinned mdformat-front-matters support so YAML frontmatter in SKILL.md remains parseable while Markdown is formatted.

Related Issue

Not linked.

Potential Risk & Impact

• Documentation and repository-hook configuration only; no runtime source code changes.
• The formatter plugin is pinned to 2.0.0 and is used by the existing mdformat hook.
• The main risk is documentation interpretation, mitigated by the owner map, historical links, and frontmatter validation.

How Has This Been Tested?

• prek run --all-files
• PYTHONDONTWRITEBYTECODE=1 PYTHONPATH=src python3 -B -m unittest discover -s tests -v (343 passed)
• Six skill frontmatter and duplicate-name validation
• Markdown relative-link validation and git diff --check