Schema current V1 contracts

Use unversioned names for current contracts (Session, Permission, Question) and explicit V1 only for retained compatibility; never preserve V2 as the permanent architecture name or make current code depend on a future src/v1/. Public contracts are readonly, omit undefined via optional(...), use Schema.Json for serializable data and Schema.Unknown for opaque data, and retain one canonical schema identity rather than bridge aliases or generation-only copies.