Governance parity: stamp standard .machine_readable + CONTRIBUTING/SECURITY/COC from standards

[hyperpolymath]

Bring this hub to governance parity with hyperpolymath/standards.

• Stamp the standard .machine_readable surface expected of org repos.
• Add CONTRIBUTING, SECURITY, and CODE_OF_CONDUCT, sourced/pinned from standards.
• Keep these as satellite references where the canonical text lives upstream.