docs: move working notes into docs-cms

[jrepp]

Summary

• convert root-level working docs into durable docs-cms memos/RFC content
• add docuchango's local docs-cms config and compressed AGENTS.md guidance
• update bootstrap guide to prefer docuchango init and clarify self-maintenance guidance

Checks

• uv run --python python3.11 docuchango validate
• uv run --python python3.11 pytest --cov=docuchango --cov-report=xml --cov-report=term --cov-report=html
• uv run --python python3.11 ruff format --check .
• uv run --python python3.11 ruff check .
• uv run --python python3.11 mypy docuchango tests
• uv build
• uv tool run twine check dist/*

Note: bare uv run is blocked locally by .python-version resolving to Python 3.9.6 while pyproject requires >=3.10, so checks were run with Python 3.11 explicitly.