Offline migration adapters

Own concrete BitFun readers and converters against shared storage contracts. No Core, product assembly, application host, or live Agent/session lifecycle. Agent Runtime may be consumed only with definition-contracts for static Agent and Skill parsing. Stored connection imports never connect to remote hosts. Keep original source-read-only behavior, atomic domain writes, idempotent journal recovery, reference repair and target conflict rules. Share storage formats with config-contracts and services-core; do not copy private application schemas.

Focused verification:

cargo test -p openbitfun-legacy-migration-adapters --lib