Companion to SDK 0.4.0 (enforcement layer) and 0.5.0 (DC2D runtime).

Includes:
- §9.5 Python SDK Enforcement Layer in the canonical spec
- Appendix §C.8 pointing at the companion docs
- docs/runtime-patterns.md and docs/framework-adapters.md
- Three reference integrations under examples/
- Updated implementation guide and CHANGELOG