Make the OpenAdapt monorepo the engine in repository metadata

[abrichr]

The engine now lives in OpenAdapt under packages/flow.

• canonical_product.engine is OpenAdapt/packages/flow.
• openadapt-flow, openadapt-agent and openadapt-types descriptions say they are frozen and point at their packages.
• openadapt-flow and openadapt-agent leave the organization pins (check_profile.py, its test and APPLY.sh updated).

The release policy files are unchanged, so current admissions still validate (7 active).